I just Beat The GMAT!

I just took the GMAT this morning and scored a 580, which is incredibly disappointing, since on my MGMAT diagnostic test I scored a 640.

My breakdown was as follows:

Score: 580
Quant: 33 (37 percentile) <---How did this happen????
Verbal: 36 (78 percentile)

I'm going to take the test again to make it for Round 2 deadlines. What is the best way I can spend my time between now and then? Go through official guides from scratch?

All of my other parts of my application will be pretty solid- this is the only thing holding me back! Help!