I'm not sure how much this helps for many people, but when I had my test, I thought of it more as a drive just to show that I'm not a bad driver, rather than being tested per se... Also, loads of people fail their tests, it's totally natural, so that's another thing, just remember that if you do fail, it's not the end of the world, and it'd just make you better prepared for next time...
My routine before the test was really important for me... Got up at a good time, had a nice shower, made sure I felt good, had breakfast, generally didn't think about it too much... I'd say if you can, get your car cleaned this afternoon, as you don't really want to be worrying about that tomorrow morning before your test...
Presuming you're driving to your test, perhaps have a quick practice of each manoeuvre on the way, and just feel in a good way!!!
Good luck