Hi candey11,
The scoring algorithm on the Official GMAT is far more complicated than most people realize. Since that algorithm is proprietary, no GMAT company has an exact match for it, thus CAT scores can vary a bit based on the 'biases' involved in their respective designs. The most realistic CATs available are the 6 from GMAC, but the CATs from Kaplan,
MGMAT and Veritas are all 'close enough' to the real thing that they will provide you with a relatively realistic score assessment (assuming that you use the CAT correctly).
The variation in these 2 CAT Scores could be because of how you took each CAT. Where did you take them? What time did you start? What section order did you choose (and did you take the FULL CAT - with the Essay and IR sections)? There are lots of factors to consider. Since your Official GMAT is in just a few days, you should NOT take any more CATs - and you should keep your studies light (so NO "cramming" either). You would be better served by doing some general review and getting some extra rest so that you can go into Test Day calm and ready to work.
As a side note, to hit your Score Goal you do NOT have to correctly answer ANY questions that you think are too hard or too weird. If you choose to review these 2 CATs, then you should note which questions you got wrong because of a silly/little mistake and which ones you got wrong because they were just too hard. Eliminating the silly mistakes is the key to hitting your Score Goal.
You should post back here after you've taken your Official GMAT and we can discuss the results.
GMAT assassins aren't born, they're made,
Rich