Don't worry, it actually happened the same to me. I sat for the GMAT on the 3rd of September and got a terrible score of 410 !!! I was so disapointed and thought of giving up on the GMAT, but this last for 2 days, and I was back on the track to blast it !!!
I took everything from the beginning, bought some books as OG12 and the Quantitative and Verbal review and the
MGMAT guides. As I was going through the books, I realized that I wasn't prepared enough AT ALL the first time. I'll re-take the GMAT on the 3rd of December and I still have a lot to go through since then but I'm feeling confident.
Just keep practicing, and focus on your weaknesses.