Hi kaladin123,
To start, a 640 is a solid Score, but the Q39 will likely be seen as a potential 'red flag' at many Programs - so retesting (with the goal of scoring higher in the Quant section) is a good idea.
Regardless of how you choose to proceed with your studies, it's worth noting that while the most realistic CATs available are the 6 from GMAC, retaking a CAT that you've already taken is NOT a realistic way to assess your skills - since you will likely see some 'repeat' questions that you have already faced. Unfortunately, seeing even a couple of repeats can 'throw off' the Scoring Algorithm and impact your pacing, energy levels, fatigue, etc. (meaning that they would likely all appear to be better than they actually are). Thankfully, the CATs from Kaplan,
MGMAT and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you correctly take the CAT in a realistic fashion) - so you can use any NEW CATs from any of those sources during this next phase of your studies.
GMAT skills can 'fade' over time. Between your two recent posts, it appears that you have not taken a FULL-LENGTH CAT since you took the Official GMAT (back in August). As such, I strongly recommend that you take a NEW CAT sometime soon and make sure to take it in a realistic fashion (take the FULL CAT - with the Essay and IR sections, take it away from your home, at the same time of day as when you'll take the Official GMAT, etc.). Once you have that score, you should report back here and we can discuss how best to proceed.
Beyond that data, before I can offer you any additional advice for your studies, it would help if you could provide a bit more information on how you've been studying and your goals:
1) Since you took the GMAT, what type of study plan have you been following? How many hours do you typically study each week?
2) What is your overall goal score?
3) What 'brands' of CATs/mocks have you used over the course of ALL of your studies?
4) When are you planning to retake the GMAT?
5) When are you planning to apply to Business School and what Schools are you planning to apply to?
You might also choose to purchase the Enhanced Score Report. While the ESR doesn’t provide a lot of information, there are usually a few data points that we can use to define what went wrong on Test Day (and what you should work on to score higher). If you purchase the ESR, then I'll be happy to analyze it for you.
GMAT assassins aren't born, they're made,
Rich