Identify your weakest problem type(s) and practice it (them). Don't time yourself, just work on understanding how to get the right answer. Obviously you should review every question you answer incorrectly, but also review every question you weren't sure about, even if you guessed correctly. Your score is dependent on how many questions you answer, how many you answer correctly (note the distinction), and the difficulty level of the questions you get right. Improving your understanding of your weakest problem types will save you from messing up mid-level questions, thereby resulting in a higher score.
If you reach a point where your performance on all question types is about equal (or if you're already at that point), I suggest improving your stamina. Three and a half hours is a long time to focus in any circumstance, and it's even worse with the stress of test day.
Good luck in your final preparations! Don't forget to sleep the night before! And bring some juice to the test center!
My GMAT debrief