With such a short amount of time left, I strongly suggest doing only official problems; in other words, the GMATPrep cats and the OG11 book. Skip the kaplan cats and any other non-official material. The only non-official material I'd recommend is the Cracking the GMAT PR book if you have no idea about the strategies for each section of the GMAT. If you already know the strategies then skip that book too.

You don't want to do both GMATPrep cats on consecutive days because you'll have learned nothing between the 1st and 2nd cat. I suggest doing the first cat immediately, then printing out all the questions you got wrong on paper (1 question per page) and try to solve each question on your own afterwards. That will force you to really try to understand the question, what you did wrong, and how you can overcome that problem next time. Then do the OG problems for most of the rest of the time you have left. Two days before the exam, do the last GMATPrep and then the repeat what you did the first exam and redo all the missed questions. This is probably the best you can do in just 12 days.