can you tell us what you've been doing? study habits? what were your practice scores?

yup..was getting a decent score of 670 average score in the manhattan as well as in kaplan test series.
but didnt cross 700.practiced official guide,then had kaplan materials also had a few books of manhattan

So if you were scoring in the high 600's on the practice exams and it wasn't translating to the real thing...Did you take the practice exams under real conditions? Timed? Proper 8 minute breaks? Essays?

yes,i did
when i started taking practice test
i took each n every test in the same gmat pattern
aftr completing 2 eassays used 2 take 8 mts brk
then quant,8mts brk
n then vrbal

how nervous were you?

What's probably happening is that you're not recognizing the material. Depending too heavily on one prep company's material can result in us getting too comfortable with the way they present information. Each prep company has a style, when given a Manhattan GMAT number properties question and a Kaplan question, odds are you will be able to tell the Manhattan question. Going forward you need to vary the tests you take. Maybe take a Manhattan CAT one week, a Kaplan the next, and a Princeton Review the next week. You want to get to the point in which you not only know the content, but also recognize what is being tested.

Thank you for the added input, osirus. I am going to try and diversify my CATs.

I think in most cases I can correctly identify a SC answer, but at the same time, I don't find myself to be comfortable with identifying the underlying error. So do I really know the material? To an extent, but there is definitely room for improvement. I really think one have to be very critical of his/her own understanding of the material, instead of just moving on because knowing the answer.