At this point, it will depend on your own objective in this process. What are you trying to get out of this GMAT? Attending a top-tier business school? Attending a business school? Use the GMAT score to attract opposite sex in the bar? All kiddings aside, think about what you're aiming for. A 300 is not a great score, but you're looking at a glass half empty. Think about the great improvement that you can have if you decide to aim for a 800.
Now, GMAT is, as you mentioned, divided into 3 sections - Essay writing (on a grading scale of 1 to 6), Quantitative section, and Verbal section. The really important parts of the GMAT are the quantiative and verbal sections, as these sections provide you with a raw score in each and these raw scores are then translated into a 800 score (this 800 score doesn't include the essay writing score, which comes separately in the official score report). To give you a quick idea, for top schools (the top 15 schools provided by US News), you want to be aiming for a 700 on GMAT (at least), which is roughly 90 percentile. For schools within the top 16-25, you can shoot for a little bit lower GMAT score and still be okay, but no less than 630 to be safe. Of course, the higher the ranking, the higher the average GMAT score. Keep in mind that GMAT is only one criteria that schools use to "judge" your application and there are numerous other factors that go into an acceptance pile.
So think about what you're looking for. And first, really consider this question: why do you want an MBA?