I rejected two DO offers a year before I got into my MD school. It was a personal decision (location, wife's education, etc), and one that I don't regret at all. As I said earlier, as long as you are working on making yourself a better person and applicant, the year or two of extra work isn't a bad thing. In those years, I met my wife, found myself, and entered into medical school as a focused assassin of the material (ok, that was lame). Anyways, I'm now a 2nd year (top 20%ile of my class), paying 1/2 the tuition that I would be at a DO school, and with more options down the road (sad but honest fact).
Good luck with your decision. Getting into a DO program with a 3.0 is not an easy thing either. Most of those schools average a 3.5.