Would appreciate some advice

Agreed with the comments above -- just keep pushing onwards and don't give up. The hardest part about recruiting as a non-target (at least from my experience) is getting the opportunity to even interview. You've broken that barrier and have gotten 6+ interviews which means that up till now you've been doing something correctly. Just because none of those have converted yet doesn't mean that you should give up trying for IB. There are a lot of banks out there that are still recruiting; you might not end up at the one you ultimately wanted for the summer (like an EB or top BB), but if you keep pushing you can maximize your chances of landing something -- remember, its still April and despite recruiting being so accelerated, it doesn't end until late summer / early fall. Just keep shooting for the stars and you'll land in the clouds. This might be survivorship basis but I have never seen anyone from a non-target who wanted banking, went ALL-IN (be honest with yourself, are you really going all-in? or is there more you could do) and NOT converted an IB offer. 

Take this weekend off, clear your mind, build your confidence backup and hop back onto the recruiting grind if its really what you want. Start plotting out the firms that are still recruiting / are about to launch their process, and start networking with the bankers there. Do exactly what you were doing before and execute another batch of calls to get into those first rounds.

Once you're in those first rounds (I'm sure you'll get at least 1 more chance), work on what you think needs improvement. It sounds like the interviews are where you get tripped up and honestly everyone has that issue. A lot of people has said this before me but an interview is a combination of preparation and luck. You can't control luck but you can control the way you prepare. 

Remember that an interview, contrary to popular believe, is less a conversation and more of a sales pitch. Might get monkey sh*t for this but at the end of the day, you're selling yourself as an potential asset to the firm you're trying to break into. I'm personally not amazing at conversation (I don't golf, I don't watch football, I haven't traveled anywhere notable in my life) and when I was recruiting a few years back, the "conversation" and "fit" portion of the interview gave me a lot of anxiety. But the important thing is to realize that you don't need to be "chatty" or have amazing "people skills" (a lot of people in banking are awkward as fck),to do well in an interview. Presence, fit and to some level "people skills" can be manufactured through proper interview preparation. 

Here is the interview prep guide for people who think they are socially awkward or are not great at conversation (you guys probably are great, you just think your not but whatever) -- prep 2 categories of things:

Soft Skills:

• Remember to display confidence when you hop on the phone or interview room (seems like you are doing that just fine given you've managed to get interviews through networking calls)
  • Way to display confidence is just to reduce filler words and talk louder -- don't end your sentences with a high pitch, control the melody in your voice and add tonality
  • A stutter here and there is fine, but reduce them if that is your issue -- unless you have a stuttering condition, people usually stutter when they don't know the answer to something or are not confident in the subject they are talking about -- that can be fixed with prep (next section)
• Remember to shake the interviewers hands when you step in the room (stand up to shake)
• Remember to sit up straight and maintain strong eye contact (but not too strong, break contact once every 4-5 seconds and look right back)
• Nod your head a few times when the interviewer is speaking and go "MHM" "MHM" BUT DON'T OVERDO IT

Hard Skills - Actual Interview Prep (Behavioral):

I realized very early on that I was TRASH at speaking off the top of my head in stressful situations (like interviews) -- if I get a question that I don't know, I will totally blank out and start stuttering while giving one word answers. This issue happens a lot more with behavioral questions than technical given that there isn't a "right" answer and its heavily experience based. 

What you need to remember is that IT IS OKAY TO SCRIPT YOUR ANSWERS. But the catch is, you can't be caught reading off it. I would type word-for-word, your answers to some of the most common behavioral questions (tell me about yourself, tell me about a time you failed, tell me about your experience at x firm) and read them aloud again and again and again until its engrained into your memory. Once you can recite the answer forward and backward without stuttering, I would layer on emotions and tonality onto the answer. Trust me, scripted answers only sound scripted when you haven't practiced the script enough. Famous actors, keynote speakers, presidents and your future MDs on calls are probably all scripted to an extent, but none of them sound scripted because they practiced their script so much it comes out natural. 

Make sure to prep the following behaviorals in a storytelling fashion:

• Tell me about a time you succeeded
• Tell me about a time you failed
• Tell me about your 3 strengths and 3 weaknesses
• Tell me about a time you worked on a team 

Prep these and commit them to heart -- every behavioral interview and conversation you are going to have is going to be centered around some variation of these 4 topics. Your interviewer might ask you this directly or in another way, but prepping these will build a strong foundation for you prior to stepping into an interview. Treat yourself like a alchemist -- those 4 answers above are different ingredients and once you have them readily available, you can easily mix them together easily to create potions that will solve your issue. Its about compiling a library of stories in the back of your head that you can easily pull to generate conversations during interviews and come off as "chatty".

After an interview, your interviewers will step in a room to discuss you and why they think you should advance / be extended an offer. On the round table, they will ask "so brad, why do you like JumboFelipe? What about him made him stand out?" -- remember, it is your job to control the narrative post interview. Do not let your interviewer draw his own conclusions about you based on your answers but EMBED those elements into your answer and spoon feed them to your interviewer. Don't say "oh a time when I succeeded was when I opened a lemonade stand and it made money" -- say "oh a time when I succeeded was back in freshmen year where I worked really hard to open a lemonade stand. At first it was difficult to run because I needed to learn how to operate a buisness like that, but I was proactive and looked on google and sht and eventually I got the hang of it, this experience really taught me how to balance multiple things at once and balance ideas" (obviously BS / strawman answer but you get the point). This answer has certain keywords in there that PRIMES your interviewer instantly -- it spoon feeds him that you are 1. hardworking 2. proactive, 3. good at research 4. can balance different things and 5. the story in itself shows that you have an entrepreneurial / scrappy spirit. 

My VP is hounding me for comments right now so I gotta duce out but hope this was helpful. As a fellow socially awkward person whos not chatty and bad at conversation, I can say this was what helped me a lot. 80% of the interview is done before the interview, 15% is execution and 5% is luck.