If you're confident that you'll do well you should go ahead and submit the AMCAS as soon as possible. But just to be safe, you can submit your AMCAS application to only one school. You'll be verified early, and after you get your scores in July you can just add the rest of the schools you want to apply to, which is a very fast process. This way you don't waste your money on all the schools if you did poorly on the MCAT (which hopefully will not be the case).