Hi Hloong99,
Working on the GMAT now - when you're not facing an immediate application deadline - is another smart choice. Raising a 500 to a 650+ (700+) will likely take at least another 3 months of consistent, guided study - and you'll have to make significant improvements to how you handle BOTH the Quant and Verbal sections. Overall, I think that you've put yourself in a really good position to hit your Score Goal, so the immediate question is really about how you would like to proceed with your studies. You already have some study materials, so there's something to be said for working with those materials first (at least for the immediate future). I suggest that you study as you like for the next 3 weeks, then take a new, FULL-LENGTH CAT (with the Essay and IR sections). Once you have that score, you should report back and we can discuss how best to succeed.
GMAT assassins aren't born, they're made,
Rich