Hi ktv,
Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so it's likely that you just have not put in enough time and effort yet to have scored higher. In that same way, the goal to raise a 550 to a 680+ in one month is likely too difficult to be considered realistic. You're likely going to have to make significant improvements to how you handle BOTH the Quant and Verbal sections - and all of that work is going to take time (probably at least another 3 months of consistent, guided study). Since you appear to be facing a looming deadline, I understand if this new information might not make you happy - but you have to remember your REAL goal: to get into your first-choice Business School. Rushing in to take the GMAT, and rushing in an application that might be 'weak' in certain spots, works against that ultimate goal, so you might want to consider a later application deadline.
1) What were your Quant and Verbal Scaled Scores when you scored 550?
2) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich