Well, you're in a pretty tough spot - 190 points in two days would be a remarkable improvement. That said, there are a few areas where you might be able to cram successfully:
1. Learn your math definitions cold - things like even/odd (test: is zero even, odd, or neither?), positive/negative (test: is zero positive, negative, or neither?), prime (test: is 1 prime?), integer, divisible, multiple, factor, etc. come up ALL the time.
2. Brush up on number properties, such as odd x odd = odd, but odd x even = even. These also come up all the time and can save you if you don't know how/don't have time to do the calculations.
3. Brush up on your basic geometry - triangles and circles, primarily.
4. Make sure you really understand the thought process in data sufficiency, particularly ones that ask yes/no questions. Understand what each answer choice means.
5. If you haven't already done so, look at the main GMAT grammatical rules. The handful of main grammatical errors come up on virtually every sentence correction problem.
In addition, know when to cut your losses in the math section. It's perfectly okay to skip a few questions that you know you won't get right, even if you spend 10 minutes on them. This can really boost your score by providing you with time on the rest of the section. You can get quite a few questions wrong and still get a 500 - so don't stress out over the harder questions and go for the low-hanging fruit.
I hope this helps, and good luck!
Jim S. - Veritas Prep GMAT Instructor (Los Angeles, CA)