EC Interview Advice for a first time interviewee

Hello everyone

I have a 1st round interview with a EC shop (think Analysis Group/CRA) on Monday, and I am nervous b/c it is my first interview for a job in the financial field. It is one of the only interviews I got through my OCR program so I definitely want to kill it. Additionally, I feel like I was lucky to get the interview since I know people with much better resumes/credentials (including two kids who got interviews at MBB) got dinged.

So my questions to everyone is this: Can anyone offer insight into the type of interview I can expect? No one on campus that I have talked to has any idea what I can expect. I've done ample research into the company, their position, strengths, etc. and am confident in my ability to present myself and my experiences (I have no prior financial experience aside from my time at a target under-grad Bschool) well, however I feel underprepared for any technical or case questions/studies that may come up.

Should I expect similar tech questions that my friends going through interviews at MBB are getting? Similar case studies? In general should I expect many questions along these lines at all? Is there any subject in particular I should focus on over the next few days in preparation?

On a final note, should I be concerned that my resume doesn't really stack up well to other applicants? I have a lower GPA then I'd care to admit, mostly owing to my over extending myself during my Sophomore year (currently junior), however I was a Varsity athlete for that time, and my grades have improved since I stopped. How can I present myself in the best light given this information?

Thank you for taking the time to read/respond to this and I apologize in advance if this seems like a repost, as I really havent come across very many insights into these questions.