Hi Michilocatelli95,
While the OG12 is an older version of the Official Guide, most of the practice questions in that book are still relevant to the current version of the GMAT, so you should be fine working out of that book at this point. That having been said, it's not clear how well you studies have been going overall, so before I can offer you any additional advice, it would help if you could provide a bit more information on how you've been studying and your goals:
Studies:
1) How long have you studied?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs/mocks (including the Quant and Verbal Scaled Scores for EACH)?
Goals:
4) What is your goal score?
5) When are you planning to apply to Business School?
6) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich