I would say, trust the GMAT prep test scores. MGMAT questions are equally tough but the algorithm is little lenient (that’s what I feel).
1 See if you can postpone the exam.
2 If postponing is not an option,
Quants: Do not concentrate on the hard quants questions, such as Probability and Permutation/Combination. but concentrate on the types which can be easily improved. Such as geometry, number properties, word problems. Do not run after difficult questions. Strengthen your basics. Even during the exam. If you think that particular question is out of your league, just guess the answer choice and move on. Otherwise you might miss 4-5 simpler ones running after the hard one. GMAT hates those who cannot manage timing. If you leave 1 question unanswered, your score drops by 3 percentile. And that’s a huge loss. So work on your timing and stick to questions which you mostly get right.
Verbal: Since you have only two weeks left, do not try any new strategy on CR or RC. Go through MGMAT’s “Thursdays with Ron” videos on SC (they are free). Also go through MGMAT SC
book again carefully. Always check for S-V agreement, pronoun error, modifier error and as-like in SC. You will be able to eliminate many answer choices by following few simple rules.
Long story short, ask yourself if the score you are getting in mock tests is good for the schools you wish to get into. If not, please postpone. If you have to give exam in two weeks, stick to what you have learnt and do your best. Do not change the game plan last minute.
All the best!