I am about to take the GMAT and after covering all MGMAT materials I am still having some problems. Any suggestions?

Please give us more detail on what you're still struggling with. Question types, content areas, accuracy vs. timing, etc.

FYI - most people don't need more materials than what we use in the program. If you're still struggling, that most likely means you didn't study everything in the right / best way the first time around. So my advice is probably going to be to go back over certain things - but I need to know what you're struggling with to tell you what to do and how to do it.