Hi irisngbonus,

Any of the recent Official Guides is a great source for practice questions, so if you already have the OG2017 then you likely don't need the OG2018 (the OG2017 and the OG2018 are remarkably similar books; with each yearly publication, the newer book 'swaps out' about 130 questions with new material). You'll likely need additional practice materials besides one of those books though, so 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?
2) What study materials have you used so far?
3) How have you scored on EACH of your CATs (including the Quant and Verbal Scaled Scores for EACH)?
4) What is your goal score?
5) When are you planning to take the GMAT?

GMAT assassins aren't born, they're made,
Rich