arnijon90,
When you took your
MGMAT and GMAT Prep tests, did you complete all the sections (Essay, IR etc) with the breaks in between as well? If not, you should do that.
Also, since your GMAT PREP scores are slightly better, had you seen any of those questions before (in forums, Thursdays with Ron etc)? If so, your scores on GMAT PREP may be inflated a little bit.
Also,
MGMAT Quant is harder than the actual GMAT's Quant. So, you could easily add another 2 points to your
MGMAT Quant score. That's not true with
MGMAT's Verbal though. It's the closest to GMAT Prep (but no way the same as that).
If I were you, I would take it easy and not be too hard on myself. Have a nice break for a week or so and give the GMAT again. Also, give another GMAT prep after a few weeks (properly timed). If possible, purchase the GMAT PREP question bank (350 additional questions or so). That is very helpful as well, given that they are totally new.
Good Luck.