Why are you taking the August MCAT and not the April. I'm assuming you need to finish up some material next summer.
If you're in the process of finishing up and will be finished by next May, then take the April MCAT.
Many schools operate on the "first come, first serve" basis. So, the earlier you get your application in, the better.
If for instance, you are finishing up Orgo and physics next semester, part 2. Then you'll be fine for the MCAT. THere might be a section or two on Nitrogen containing compounds that you haven't finished or something like that, but you can read it on your own. Get a good MCAT review book and learn the basics. You need practice and a rudimentary understanding. The MCAT is mostly applied analyses.
Since you're applying DO. If you haven't already, shadow a DO or two. Get some letters from alum, that's even better. Contact the school that you're interested in. Set up a time to visit, go to open houses.
Apply early next summer, you'll have your secondary in by July and interview in Sept.