You will spend some time before your test with your instructor and that they will work with you to fine tune your performance on the day. They know that your state of mind is as important as your general driving standards.
Your instructor has come to know you and knows how you will be on the day, they can take a pretty good guess even before you come out of the house. They have seen you in stressful situations before. Do you remember the first time that you pointed the front of the car at a major roundabout looking for a suitable gap?
In the trade we usually expect that test nerves will reduce the effectiveness of our pupils by up to twenty percent. We balance this by aiming higher than the minimum acceptable standard before we put you in for it. Everything possible has been taken into consideration without you having to do a thing.