Hi shagalo,
If you've only been using the OG for practice, then chances are that you're going to have to invest in some additional practice resources.
Have you taken any FULL-LENGTH practice CATs yet? If you did, then how did you score? If not, then there are a variety of sources that offer reputable CATs. I can't stress this enough - to properly prepare for the Official GMAT, you MUST take the ENTIRE CAT each time.
You can download 2 practice CATs for free from
www.mba.com. That same site offers two additional CATs that you can purchase. You can also buy "blocks" of CATs from
MGMAT, Veritas and Kaplan (the CATs come with some of the Kaplan books). It's worth noting that taking LOTS of CATs is not what will make you a strong Test Taker. You should take a certain number of CATs over the course of your studies to gauge your progress, but the real improvements come from practice and review.
GMAT assassins aren't born, they're made,
Rich