IMHO, you shouldn't do this. You probably don't have enough time to study and get into the 'GMAT frame of mind'.
If I were you, I'd study from Kaplan
/Peterson's (but not the official guides) for a week, download and install the GMATprep software from the GMAC website, and take a complete diagnostic test using this software. If you score 700+, you have a decent chance of hitting that score. If not, I would study longer and apply for the MBA next year, or in the 3rd round (June?).
Hope this helps,