doomedcat, you mentioned that your mocks were in the 650-680 range. What is your target score? And what were you doing to study before you scored the 550?
I'm assuming this was the first time that you've taken the official GMAT, is that correct? If so, then test day jitters may have played a factor in the lower-than-expected score, but that should not affect your total by 100-130 points. It's difficult to properly assess what went wrong and how to improve without more context and data, but don't get your hopes down. If your practice tests were consistently in the mid-high 600s, then there's no reason you can't hit or surpass those scores the next time around!
It might be worth giving yourself more than one month to retake it, but it sounds like you are set on that timeframe. Either way, feel free to check out ORION if you're looking for personalized and structured support. ORION uses computer-adaptive technology to diagnose each student's strengths and weaknesses and only serve up skills and strategies catered to their weak areas, in turn maximizing the return on their study time. It would be a great resource for someone like you who only has one month to improve their score. Let me know what you think!