I had similar problem during my mock test and initially on the test too. But my inspector said was nice and made me feel at ease. But a couple or three weeks back I did my mock test and failed because I was nervous. So pleas drive more with person you would feel at ease and that will improve confidence. During normal driving training, put yourself in different situations so you are prepared and know what to expect and how to react. My driving instructor said I should think of the whole thing as a road trip. But it did not work for me. Maybe it will for you
But I think you should try to calm yourself down in the car before you leave, after your safety check. If you think you will be stuck in situations that will be stressful to you, maintain a speed where you will be confident first and once you have gotten into the rhythm then you will be more comfortable driving. Finally, even if you make a small mistake or two, it is ok as far as you’re driving safe - in a way that is adapted to the condition of the road and not dangerous to other drivers. So it you do make a small fault in the test, try not to think about it so much. You could also ask the examiner if you could use the audio system to listen to your favorite songs if that will calm you down.
Best of luck!