Hi aditya432,
GMAC has publicly stated that a Test Taker's Official Score on Test Day is within +-30 points of actual ability. Assuming a similar "swing" in the accuracy of CAT scores, all of your scores are within +-30 of a 670. In that way, your scores don't vary THAT much, even if that's how you're interpreting the numbers.
The good news is that you're fairly close to a 700+ score right now, but at this scoring level, the GMAT becomes really "sensitive" to little mistakes, so you have to find (and "fix") those mistakes to improve your scores.
To that end, on your last CAT, how many questions COULD you have gotten correct, but did NOT (for whatever reason)? THOSE questions represent most (if not all) of your missing points. You might be able to self-train to "fix" all of those issues, but if you can't do it on your own then you'll need to invest in some new GMAT resources to help you learn some new tactics.
GMAT assassins aren't born, they're made,
Rich