....another problem with me is taht i become exteremely nervous while giving d exam...
It is again good news that you are aware of another weakness.
Mind game is important - you have to understand where your anxiety comes from, and address those effectively. Some anxieties cannot be eliminated, so the approach is to reduce them.
So why are you feeling nervous during the exam?
Many people here took tons of practice CAT tests before the real exam (just search under GMAT experience). So you should do the same and that usually help. You will also found some test strategy improvements by doing such exams.
Try to simulate what will happen on a test date: Pick a date and imagine that is your test date, do the exact things you would do on the actual test date. This is a easy strategy to help reduce stress on the actual test date.