Hi pm1798,
Studying for the GMAT now - far in advance of when you will actually 'need' your Score - is a smart choice. If you are concerned about your general 'math skills', then you might want to focus on those skills first before you commit to working on your GMAT Quant skills (since those require a mix of math along with Quant Tactics, pattern-recognition, etc.). For free math practice and help, I recommend that you set up an account at Khan Academy (
www.khanacademy.org). The site is completely free and makes the learning a bit more fun and 'game-like' (as opposed to the dry academic approach taken by most books). While the site is vast, you should limit your studies to basic Arithmetic, Algebra and Geometry. After spending a little time re-building those skills, you can jump back into your GMAT studies.
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) How long have you studied so far? How many hours do you typically study each week?
2) Have you used any other study materials besides the Official Guide? Which OG have you been working with?
3) Going forward, how many hours do you think you can consistently study each week?
GMAT assassins aren't born, they're made,
Rich