If you really feel that your score will improve at your next sitting, spend your energy figuring out what you need to do to improve rather than on worrying about what's already done. If you feel that your score does not reflect your ability to exceed at a graduate level (which is obviously the case or you wouldn't be applying), consider sending those schools a paragraph of "additional information." Let them know that standardized tests are not your strong suit (maybe you didn't do so hot on the SAT, but your undergrad GPA is high and you had a lot of ECs). You are planning to retake the test and you hope that your score does not detract from XYZ better parts of your app. blah blah. Adcoms are human too. At the end of the day, they want students who WANT to be at their schools, so show them some effort. There's no guarantee that they won't use the score against you, but at least an explanation might give them a different perspective and make them think twice.