Best of luck Matt. Don't put too much pressure on yourself, it's not life and death.
When I did my bike test, I was an absolute nervous wreck and I was paranoid about doing something daft. I rode to the test centre with my instructor and another pupil. This other guy was über chilled out, it was driving me mad! Whilst waiting to be called out (I was going the be tested second so had an agonising wait) I asked the guy how come he was so relaxed. He gave me a super smug look and said he was a armed response police officer, trained for stressful situations so this was a piece of cake. 100 yards into his test he went to pieces, jumped a red light at a pedestrian crossing nearly wiping out a pensioner in the process.
After he returned to the test centre in pieces, I almost resigned myself to not passing, relaxed and as a result rode nearly perfectly passing with one minor (arguable) mark on my test sheet.