So you didn't make the MD and aiming to have a DO backup at this late in the game? Join the crowd of 1000's of scrambling and desperate MD applicants! You should have done this early Dec. at the latest. It might be 2 weeks and it might be 6 weeks, either way you are best case at the bottom of the list of 1000's sometime in February.
Unless you have a ~4.0 and 515 MCAT, you are potentially throwing good money away and even then it's a toss up. As an adcom I'd wonder then why MD schools didn't want you, but I'm guessing you are on the low side of stats for an MD? IMO get things in order and be an early applicant for next cycle. Fix your deficits and reapply to both MD (if you have the stats) and DO next time. Or apply and have a snowballs chance to get in (Do you feel lucky?) or risk being listed as a re-applicant.
Best of Luck!