RaichuGirl, if you keep that attitude up, you probably will.
Try to stay positive. Believe it or not, mood actually does influence performance. Think of what you do know, and read up on what you don't. But above all, try and keep a smile on your face, or at least in your head.
I know, I've been there. If you feel negatively about an upcoming test, you're already in a bad frame of mind to be taking it. Just prepare yourself as much as you feel you need, and go in optimistic.