God, do I know that feeling.
Let me tell you something. I worried about entry exams to engineering school last year. I was constantly in a state of readiness and panic, until it was over. I worried a lot. And... I messed up bad. Exactly 50/100 points, all things combined. 50% correct answers.
So it's good that you worry. Keep studying, because I didn't study for a goddamn day, and it brought me a lot of grief (although I did get into engineering school). Just don't worry too much. In the end, there's only so much you can do, so let the cards fall where they may.
Good luck!