This is exactly why I have a policy of not studying the day before an exam. I front load all my studying. I would study like crazy the first week of the month. Still pretty hard the next week. Start reviewing the next week. Then have a light week for the week of the exam.
Before I adopted the front-loading studying schedule, I would freak out before an exam. I would see one random, irrelevant fact the day before and exam and freak out, convinced I was going to fail. For this reason, I wouldn't even hang out with my med school friends that day.
Also, for some odd reason, whenever I started a test, I would always see the first question and freak out. I would think "Oh no, I didn't study enough. I'm going to fail. I shouldn't be in med school. Theyre going to flunk me out." I would calm down, go to the next question and just keep going until I found a question that I was 100% sure on. That would give me the confidence I needed to get through the test. This may sound odd, but I swear I felt that way on every test I took (including both Step exams).
You'll be fine. Relax. Avoid high strung med-student friends. And have a nice workout/run/something stress relieving after the test then go out and have a few beers.