I would not recommend taking the GMAT again in two weeks if you just scored in the 300s. Work the material, starting from a basic book, and improve your test taking strategy. Retaking the test over and over again with poor results is only going to frustrate you and make it hard to achieve a really great score.
Do you have any sense why you scored poorly? Were you constantly running out of time, were the early questions too difficult, etc.? If you have a sense for what your greatest challenge is moving forward, you can probably make significant improvements by focusing on that first. For example, if you're failing on the first few questions, it doesn't matter how well you do later in the test -- you will be sunk by screwing up the early ones.