Hi shrutya,
A 640 on your first practice CAT test is a really strong performance (the average on the Official GMAT tends to hover around 540-550 each year). With a Test Date in early February, you don't have much time to study, so you'll have to be efficient with the time that you do have. I have some questions about how you've studied so far:
1) What were the Scaled Scores (for the Quant and Verbal sections) on this CAT?
2) Did you take the ENTIRE CAT (including the Essay and IR sections)?
3) How was your pacing on this CAT? Did you finish any sections early or have to rush at the end just to finish a section?
4) What materials are you currently studying with?
5) Do you have any areas that you consider to be "weak spots"?
6) When are you planning to apply to School?
GMAT assassins aren't born, they're made,
Rich