Hey Soni,
The only thing you have to fear is fear itself! The official GMAT comes with a margin of error of 20 points (GMAC admits that if you score 700 it could really mean that you're a 680 or a 720), so your fluctuation is well within the margin of error. And there are other pretty valid explanations, too - did you take those tests under different conditions? Were you worn down from a week of studying when you took the second one? Did you pace yourself differently or make a couple extra careless errors the second time?
Keep in mind that there are a lot of potential factors that could impact a small swing like that, and the vast majority of them aren't anything to worry about. PLUS - you now have a blueprint of what happens on "a bad day" for you, with your 650 score report. You can go back and analyze what was different and learn from it. Did a time-intensive geometry problem cost you a minute or two early in the test and force you to rush and make careless mistakes? Did you lose concentration in the late teens of either section and miss 2-3 questions in a row between question 17 and 20? Did you miss a couple Pronoun errors while you were chasing something that seemed harder?
Learn from the 650 - if you have to have a bad day over the next week it's a whole lot better that it was yesterday than test day!
Brian Galvin
GMAT Instructor
Chief Academic Officer
Veritas Prep
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