Once you start at any US med school, and they know that, they will be very unlikely to accept you if they know you are already attending somewhere else. Did you not apply to MD this year? If you only want an MD, it might be better for you in the long run to just hold off attending the DO school and reapplying MD, especially if that is your plan to begin with. Good luck.
Edit: I also wanted to add that it would be significantly cheaper to just rewrite the boards after getting your DO, rather than paying for an extra year of med school. The costs of this would be very discouraging if nothing else was...