I don't think taking anatomy is a bad idea. I don't know that it will help your grade in anatomy when you get to med school, but as someone who took a few years off between the last time I was a regular student, and the beginning of med school, I can tell you that there is something to be said for staying sharp.
So yeah, take the anatomy. Learn it as well as you can. Go far beyond the scope of the college course, get BRS gross anatomy, and see what you can accomplish.
It won't be the same, but I think this is not a bad idea.
Having said that, there is also something to be said for enjoying yourself this last summer before med school, and I would hardly hold it against you if you decided to spend it working out, going to the lake, drinking beer, and so-on.
Do whatever you want. I don't think that this is necessarily a bad idea at all though. Again, I don't necessarily affect your grade, but it may help your overall comfort level with the material.
I should add that it is unlikely that you currently posess the capability required to learn this material at the level necessary for med school. That is provided to you with the first lecture packet. You will not be able to force this yourself. It comes naturally with the challenge.
Do not convince yourself that you are studying ahead for anatomy. Think of it as more of a familiarization process. You cannot study ahead. Hell, I've taken exams in the morning and gotten an A, and I'm sure if I took the same exam the next day, I'd fail. Never mind trying to remember **** from months before.