First of all. Breathe, calm down and RELAX. The one thing that IS going to affect your performance is your attitude and confidence levels. Granted, no one is going to go in with a big grin on their faces, but try and avoid going in with an idea of what you're going to come out with, e.g a pass, or fail, etc.
You must remember reivising TOO MUCH is not advised, since stress levels increase, therefore your concentration levels will deteriorate fast. So, relax. Have a bath or shower, or put on your favourite music or TV show and have a good laugh or watch some funny TV.
If you've done the work, regardless of what your past papers are telling you, it does not matter. You will be fine. Panicking and stressing will make the experience a negative one - try to turn this into a positive one, like a learning experience, or the start of a new attitude towards examinations.