Hi SonGoku,
Since you are not planning to apply to Business School for a couple of years, you have plenty of time to continue studying - which is good. Unfortunately, you will likely need far more study time than you have allotted (for your August Test Date), so you might want to consider pushing that Test Date back. There's no 'harm' in taking the Exam at that point, but you could save some money - and some frustration - by rescheduling.
As far as the variations in your Test Scores are concerned, it's important to remember that Test Day is a rather specific 'event' - the details are specific and they matter, so you have to train as best as you can for all of them. The more realistic you can make your CATs, the more likely the score results are to be accurate. The more you deviate, the more "inflated" your practice scores can become. As such, we should examine how you took each of your practice CATs:
When you took your CATs:
1) Did you take the ENTIRE CAT each time (including the Essay and IR sections)?
2) Did you take them at home?
3) Did you take them at the same time of day as when you plan to take your Official GMAT? What time did you take the Official GMAT?
4) Did you ever do ANYTHING during your CATs that you couldn't do on Test Day (pause the CAT, skip sections, take longer breaks, etc.)?
5) Did you take any of these CATs BEFORE? Had you seen any of the questions BEFORE (re: in an online forum or in a practice set)?
GMAT assassins aren't born, they're made,
Rich