Just seen this, a bit late in the day.
As said above, try to relax. Easy to say.
Remember, the examiner is on your side. It is all the people outside that are out to get you. Examiners come to the job, like instructors, because they love driving, and want others to love it too, and be safe. They don't fail you, only you can do that, they just observe.
If you think, at any time, that you've made a mistake, forget it, and carry on, concentrating as you go. If you believe you've just failed, you'll then make mistakes that will fail you. Seen that happen too often. Had a few who thought they had failed, relaxed, and drove much better. Their 'fail' reason turned out to be trivial, and in two cases, not even noted as a fault.
Look well ahead, keep space.
If you find yourself in the wrong lane, go where it takes you. No-one fails for taking a wrong route, lots fail for trying to fix it. Being lost, safely, is fine. Being on the right route, unsafely, is not fine.
Don't think about the passenger as critical, just someone to take for a ride, and show off how good you are.
Slow, and safe, are not the same word. Go with the flow. (As long as the flow is at a legal speed.) Moving away from a junction briskly is often necessary, so don't be afraid.
If you're not sure of an instruction, don't be afraid to ask the examiner to repeat it.
As you are taking the test in your own car, I'm guessing an instructor is not involved tomorrow. You will need an extra mirror inside, for the examiner. Hopefully whoever has been helping you has one already, if not, Halfords will charge you a small fortune for one, any other car accessory shop will have one at a more reasonable price. Check it sticks to their window before leaving the shop, a a few have duff suckers. Can test on any glass surface, even their display cabinets. My local accessory shop is used to me doing that now.
Good luck, let us know how it went.
If sadly, it is a fail, let Mum/Dad (whoever) listen to the debrief, so you can think about it later. You'll be emotional, and will not retain the information. Whoever accompanies you there, let them drive home, whether you pass or fail. Emotions will get in the way of a safe drive home. You'll see all the instructors driving out afterwards.
If it is a fail, and you don't have an instructor to discuss it with, send me a PM, I'll happily help where I can.