I took GMAT on october 10, not long ago, and scored just 610. I was not much frustrated because I felt that I am not yet ready to cross that desired 700 barrier.
But on the test day, I had confidence and concentration. Of course, noise coming from all over the keyboard around you will disturb you, but if you put the earphones, which are noise proof, and concentrate on your test you can do your best.
On the test day, I was thinking I could maximize my potential, which was way more than 610, but I could not.
And here are the reasons:
1) Overconfidence
2) Being too calm
3) Getting frustrated by few difficult questions
4) Lack of preparation 10 days to test
I am sure if you are confident, but not over. calm but not too calm, and is not frustrated by few difficult questions you encounter at the beginning of the test, you will be able to maximize your score.
And do not get lazy few days to the test, as I was, review your weakest points. And do not do any test one day before the test day.
These are the few tips, I can share with.