I appeared for my GMAT test on 2nd of July-20. Though I was very nervous for my exam(almost everyone is), I had just remembered one thing that I would give my best. The most important thing to remember is you don't have to start analysing your performance in between the exam. I did the same in my previous attempt(in the month of March-20). In between the exam, I started thinking that I am doing very good, I would definitely cross 700 level, but I actually ended up scoring only 620.
This time I had decided, I would not repeat my mistake, I wont just think anything during my exam and will just give my best. There were times in between, I started thinking that oh.. I am doing very bad. This time also I will score around 600. But I controlled my thinking and focused on my questions. I finally scored 710 (Q-50, V-36).
So, moral of the story is
just don't think about how you are performing while appearing for the test. Even if you think that you are performing very good or very bad, you will never know your actual performance until the final score comes out.
P.S. Just watch some funny videos or movie scenes before your exam. It lightens your mood and really helps.