Cannot stop worrying about permit test?

I am usually a very confident person with straight A's in school but each time I have gone to the DVM to take my permit test I froze with nervousness. Tomorrow will be my third try taking it and although I have studied harder than ever I still feel I will do terribly. In my state there are many trick questions and I find myself second guessing a lot. Even the room makes me freak out. It's in the middle of the waiting area with each side being a glass wall where everyone can see in and stare at you, making me feel very pressured about how long it takes me. It's been looming over me for some time now and I feel sick even thinking about it, I feel as though I will vomit when I'm actually there. How can I feel less nervous?