then I went away and did not study for about 3-4 weeks
You'd be amazed how quickly you lose the material. If you stop doing anything for a month, you'll lose your skills. You need to get back into your daily study regimen - from now until the test, every day (or almost every day).
GMATPrep doesn't give you any feedback about your strengths and weaknesses so you'll have to go pull it out yourself (or you can take another MGMAT test and run the assessment reports). Go figure out what's still okay and what's not okay and use that to set your study priorities.
Also, if you aren't taking the test for another 2 months, you need to review absolutely everything in that timeframe - anything you don't review from the class, you will not remember 3 months after the class ended.
For others reading, if at all possible, try to take the test within about a month of finishing your course - and study daily even after the course ends. Otherwise, you'll start to forget things!