Hi jrrs,
Many Test Takers spend 3 months (or more) of consistent study time before they hit their 'peak' scores, so it's likely that you just have not put in enough time and effort yet. If you want to take the GMAT in the latter half of September, then you would be giving yourself just 1.5 - 2 months of potential study time - and that would likely limit how much you could improve. It would also help to define your Score Goal (if possible) - since it's quite helpful to have something to compare your practice results to.
Since it sounds like you're just beginning your studies, then it would be a good idea to take a FULL-LENGTH practice CAT Test; you can take 2 for free at
www.mba.com (and they come with some additional practice materials). If you want to do a little studying first, so that you can familiarize yourself with the basic content and question types, then that's okay - but you shouldn't wait too long to take that initial CAT. That score will give us a good sense of your natural strengths and weaknesses and will help provide a basis for comparison as you continue to study. A FULL CAT takes about 3.5 hours to complete, so make sure that you've set aside enough time to take it in one sitting. Once you have those scores, you should report back here and we can come up with a study plan.
GMAT assassins aren't born, they're made,
Rich