Hi lbbdow,
First off, a 680/Q48 is a strong score (it's right around the 85th percentile overall), so it could very well be enough to get you into your first-choice School. As such, a retest might not be necessary. Depending on the Schools you plan to apply to, you would likely find it beneficial to speak with an Admissions Expert about your overall profile. There's a Forum full of them here:
ask-admission-consultants-124/From the information provided, you've taken 7 CATs and the Official GMAT in just over 3 weeks. The reason why your scores are all 'clustered' in the mid-to-high-600s is because you have not given yourself enough time to properly change your habits, practice and improve. Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores. During that time, it's important to take FULL CATs at regular intervals (1 FULL CAT every 1-2 weeks) - so that you can spend the bulk of your time learning/practicing the proper Tactics and honing your skills. The act of taking/reviewing a CAT requires a great deal of effort and energy; by extension, it also takes a certain amount of 'recovery time.' Studying "your way", you haven't given yourself the necessary time to score higher.
Given this pattern and your score goal, I highly recommend that you push back your Test Date and study in a more reasonable, guided fashion. You can certainly take the GMAT as scheduled, but you'll likely score in this same general range (which will mean that you'll end up taking the GMAT a third time later on this Summer). With the right materials and a different routine, you could conceivably hit your score goal in a month, but you'll have to be flexible enough to make the necessary changes to your routine.
1) When are you planning to apply to Business School?
2) What Schools are you planning to apply to?
GMAT assassins aren't born, they're made,
Rich