There shouldn't be such difference between GMAT prep and
MGMAT tests score. The Quants in
MGMAT is little tough. Verbal is at par. Did you analyze your mistakes well? Were all pf them silly mistakes? If they are conceptual errors, you can improve on them. Silly mistakes are scary. You have to be more attentive.
I'm in the same boat. Taking GMAT on 24th April. I too made lot of silly mistakes and calculation errors. But then I found pattern in my mistakes. Most of them were in inequality problems. I dont like those. So whenever I get those I panic a little and mess up. So I started working on it and improved.
Now I make less mistakes. Gist is, try to find pattern in your silly mistakes and work on it!
And yes, we can!