As an examiner my advice would be to fly each small segment of the test to the best of your ability and forget what went before. You can't correct what has happened so make sure that the next bit is as good as you can make it.
No examiner expects perfection - If we did there would be no pilots!
Remember - With a ground exam you start with a failure and have to accumulate enough correct answers to justify a pass - With a flight test you start with a pass and have to accumulate enough errors to justify a failure.
Good luck.