Hi shravanthim,
A 120 point improvement in one week is NOT common, so we should 'nitpick' this situation a bit.
First, skipping the Essay and IR sections almost always leads to an 'inflated' score (since you're not as fatigued as you would be by taking the FULL CAT, you are more alert when you hit the Quant and Verbal sections). If you have previously seen any of the questions, then that would also lead to an inflated result.
Second, the 'biases' that occur in all GMAT company CATs may have ended up scoring you lower than your actual ability (meaning that your 590 was too low relative to your actual skills).
Third, there are a variety of details that impact a CAT performance (and how realistic the result is) that you have not described: time of Test, if you took it at home, if you did anything unrealistic while taking it (pausing the Test, listening to music, etc.), etc.
From here on out, you really should focus on making each CAT "event" match up with Test Day in as many ways as you can reasonably control. If your practice CAT scores are not accurate, then you won't have a clear understanding of what you'll need to focus on as you continue to study.
GMAT assassins aren't born, they're made,
Rich