Don't worry, you'll be fine. Your instructor thinks your ready, otherwise they wouldn't have said to book the test. The odd mistake is not the end of the world, even on the test day.
I felt anxious on the day, best tip I can give is get the anxious energy out. Do press ups, star jumps, some silly stuff like dancing or air guitar. Scream out some positive affirmation, or scream in general or sing your favourite song. Use the excess energy, it will draw the adrenaline down. Whatever you need to do, to get it out. and drink some lucozade, the sugar will help calm your nerves. I saw it in Taken and its true, your body is in a similar state of shock and the sugar will help balance you out and might help with the nausea and diarrhoea too.
Not to manifest it, but also, worse come to worst, if you dont pass you do it again. I think I passed on my 4th or 5th go and once you have your license no one cares.