I'm really worried about turnitin.com and I don't know what's wrong!?

So, my teacher called me out of class telling me that i got a 64% originality on turnitin.com! And over 40% of it is from "other papers at my school". It's also ONLY on 2/4 research papers we had to do, the other 2 were only 5% and that's because of my quotes and stuff. I never gave anybody my research papers (it was 4 turned in at the same time), and I never cheat on anything! I'm a straight A student, and got accepted to the school I dreamed of going, I don't think I'd jeopardize that by cheating and knowing it was going through turnitin.com. The teacher won't even tell me who's paper is similar to mine, and it's from another class. I have no idea what's going on, and I have to "prove my case" that I didn't cheat. Only thing I have is that 1. I have all my citations and how I got them 2. I have a certain writing style, and if I would of plagiarized, it would of been very obvious, and 3. I kind of messed up on my work cited a bit on my first 2 research papers I realized. I have no idea what's going on, and my teacher won't believe me that I didn't cheat because "she doesn't know me". I'm freaking out! If I get an F, then I get an F in the class which means I"ll get my acceptance revoked and get a referral, which means I won't get to walk for graduation!