Am I average, above average, or smart?

I'm having emotional issues and have been constantly thinking about this issue for about a year now when ever I have free time. I just can't decide whether or not I'm smart enough. I'm at the end of my freshman year. It's just sometimes for some subjects I will study hard for a test like for 3 solid hours for 2 days right before a major test. I would get like 88% instead of a 95% like some of my classmates and I really can't tell if they study or not. Sometimes someone will say they I didnt study at all. This happens to me mainly in biology. I am good in math like geometry and if I paid attention in history I tend to get an A without pretty much any studying. Another problem i have is self confidence sometimes I get so scared while doing a test that I will forget what I was thinking an instant after the thought came to mind. This tends to happen when I write essays too. What is wrong with me? I can't help but keep comparing to other people around me because I really want to be an achiever! And I'm not trying to be arrogant but I can kind of feel that I have a pretty bright mind compared to most people around me. But I just doubt myself so much that I cant make up my mind, its like I dont know myself at all. I feel completely lost and dont know what to do. I know I talk so much but I dont know how to get my feelings out by talking to someone because im afraid people will jusge me too! I feel so bad and I'm the type of person who never stops thinking!!!