you know I would almost venture to say that it would be best if you:
filled out everything in AADSAS and sent all LOR's and transcripts now.
Study hard and take the dat in about 3 weeks. I think you would have an easier time getting in with say, 18's now then with 20's in december. Plus 3 weeks of good studying is probably going to get you far enough to do very well.
Remember that right now if a school has, say, 100 spots, all you have to do is fit the norm to get in. But if by December it has already filled 70 of the spots, they will only take the best of the remainder, which may be a lot more competitive than trying to get in now.
Some schools send out plenty of acceptances knowing that a lot will opt for some other school. Don't let the adcoms get to where they can be picky about the remaining students.