You may want to push your test back, but not by too much. It's always a good idea to plan for the possibility of taking it twice, in case you don't get the score you want the first time (it's more money and time to invest, but it's worth it, right?). If your deadline is April 1, you should consider taking it the first time in late Feb, then again in late March. If you get the score you want the first time, you obviously won't have to take it again!
The first thing you should do (if you can... if you saved the questions you got wrong) is review that practice test in a lot of depth. Which areas need more work? Make a list of topics for which relatively low time investment will yield high returns. For example, if there are geometry or grammar rules that you forgot / didn't know, learning those will make a significant difference. If, however, there are general question types (such as reading comprehension or quant world problems) that give you trouble, those are harder to improve in a few weeks. Try to maximize the "improvability" of what you study.
If you finished with 30 min to spare out of 75, you're certainly moving way too quickly through the verbal section. You were probably jumping to conclusions, or missing key pieces of the questions.
The Critical Reasoning questions on the GMAT are pretty similar to LSAT questions, so make sure you're applying the same kind of reasoning there. Sentence Correction, however, is not at all like the LSAT, so this is an area that you probably want to study in depth. I'd recommend buying a SC guide, to make sure that you know your grammar rules and common patterns.
Good luck!
Ceilidh Erickson
EdM in Mind, Brain, and Education
Harvard Graduate School of Education
