From your post, I think the problem is not with the books.
But since you've taken it, it is time for you really to treat it importantly and get serious about it for the next time. Although it is not your dream score, you are familiar with the exam environment. It is what you have gained.
so get good books, focus and be really serious with the GMAT, then eventually it will reward you.
MGMAT books are quite good.
For math basics, Kaplan premiere 2007 has a very good math appendix section that lists out all the basics you need to know. It is better than the OG math basics which is not written to be understood easily.
MGMAT books may cover it as well, for you to find out.