Exams suck, don't know what else to tell you bout that, except that if you've studied you shouldn't really have much to worry about when taking it. You're getting to the point of worrying about worrying. Not a good cycle, I know that from experience. I'd just walk in the exam, tell yourself you've studied and you'll be ok, and if put all your attention on the test and you can get done and walk out of there a lot faster, go home and relax and be done with it.