High School Student

tl;dr: You need to haul ass if you want to transfer into a respectable target given your high school grades. 

So I had mediocre grades too - albeit not bad as yours - back in high school and pulled off a first year transfer. I transferred from a school ranked around ~60ish to a Duke/Brown/Cornell/UPenn. The following is what I did in order to be successful as a transfer.

Since IB recruitment is highly accelerated these days, you need to transfer after one year in order to be eligible for OCR. That said, there's a catch for first year transfers. Since most transfer applications are due in spring semester, almost all colleges (at least the 15 or so semi-targets/targets I applied to) will ask you for your high school transcript and test scores because they'll only be able to evaluate you on your first semester of college coursework. In other words, they're really evaluating you as if you're an extension of a high school applicant, except you have some college grades. 

Now the question is, how do you convince the admissions committee that you're competent and not the same idiot who blew off classes in high school? So for me, I did anything and everything in that first year of college. I took 19 credit hours of classes, got a 4.0, retook the SAT Math 2 during finals week of college, and gained as much meaningful leadership in clubs during that first year. I picked two professors who I really liked during my first semester and built strong relationships with them during office hours. I asked one of them if I could assist him with research and committed to that in my second semester. Both of them wrote me extremely strong letters of recommendations as a result. Doing those 15 transfer applications on top of everything else ate up a ton of time. (I still hate you UChicago for making me write two 650 word essays on why I'm like a potato or some bullshit). At the time, it was definitely psychologically painful. I remember sleeping maybe 4-5 hours per night, including weekends and sometimes slept at the 24/7 library on campus.

So you probably get the idea of what needs to be done in order to transfer given your circumstances. Also, the school name brand of your freshmen year institution matters a significant amount too. When I got admitted to several schools and got added to their respective transfer orientation FB groups, I noticed that almost all of the kids in the FB group came from "peer institutions". In other words, let's say for example I transferred into UPenn. Almost all of the kids in the FB group for transfers came from Michigan, Duke, Brown, Cornell, Notre Dame, Georgetown etc. I even calculated it out - it was around 90% of the kids in the FB group came from schools ranked in the top 20 or other top LACs. The remaining 10% were athletes, kids with exceptional hooks or backgrounds, URM with average profiles, and people like me. And even then, I learned during orientation that the kids who came from peer schools still came in with 3.8/3.9 GPAs so you're really not afforded with any room for error given your competition. 

You didn't ask this question but if you were to ask me, "Was it worth it?", I'd say 100% yes. There's such a huge difference between attending a complete non-target for all industries and a target for almost all industries. Even beyond just having a solid chance at going into consulting or high finance, I'm afforded the opportunity to move myself around different cities with relative ease. Meaning, while my friends at my old school would have to hustle much harder than me to move to NYC or some other major city, my school's alumni and like many other targets' alumni are all across SF/NYC/Chicago/etc. And if they're at a company I'm interested in trying to get a job at, most of them are in the right positions too due to their pedigrees (i.e., elite undergrad, former IB/PE/consultant, top MBA), so getting the interview isn't terribly difficult. 

Hope this helps you and anyone else who's in a similar position.