Settling to the Bottom

I'm scared. I'm legitimately scared. I've been reading my orgo textbook, and I understand only the major concepts. I completely don't understand most of the structures, and the ones I do, I barely comprehend.

I've always been at the top. I've been good at most of the things I do. Top in my class, top in the school. Involved in tons of activities and handling them fine. A role model, someone people go to for help and advice for everything. Curve-setting, straight-A student. I came to terms with the fact I won't be the best at Princeton. That I knew before I applied. I know I'm considered average at Princeton. But now there's the very real possibility that I won't just not be at the top, I'll be at the bottom. Who am I to compete with these star athletes, Intel/Siemens winners, national champions of this and that? Do I belong here? I really love Princeton and I'm absolutely overjoyed at having got in and being able to go, but am I worthy of it? Someone apparently thought so, but on what did he base his decision?

Can I survive there?