Try and stay as calm as you can, I know it's hard, I was so nervous, but there's some great advice here.
Disaster stories to cheer you up:
I was driving my own car on the dual carriageway and my L plate blew off. Examiner got me to pull over and replace it with a spare, set off again, all good... except that the spare then also blew off.
The examiner refused to drive my car, made me walk back to the test centre, up the side of the dual carriageway and a steep bank.
I then had to collect my dad and then walk back down the dual carriageway to my car.
When I went back for my next test THE SAME MAN came out and informed me that due to a strike, there weren't enough examiners and my test was cancelled.
I gave up for a good while after that. When I went back to it I had a few lessons with another instructor. I told him the story of my previous tests he said "OH MY GOD, that was YOU? Everyone heard about that, I can't wait to tell them I'm teaching you now" 
You'll be fine OP, good luck!