My tips:
get some exercise today, and if you find that makes you feel better, then do it again tomorrow morning before the exam.
Find some fun stuff to do to take your mind off the exam for the next few hours.
Tell yourself you can do this. It's not so bad - there are HEAPS of kids out there who are in a much worse position than you are. Acknowledge the nerves, don't try to stifle them, but just confront them. Visualise yourself being calm, confident and doing well. You know the format, you've done this before, you can do it again.
If it helps, do breathing/relaxation exercises.
Before the exam, try and take your mind off the nerves by being around supportive friends, or the fun, talkative kind of people who will make you laugh. Steer clear from the stressed out kids or those doing last minute exam prep. Hang out with the confident, happy, people and try to be one of them - confidence is key.