DO cycle runs later, so you should be fine, but you are unlikely to have any MD As by November (very few are issued by then), so you have no reason to wait if you want a greater assurance of going to med school next year. If you don't like DO, you don't have to go that route. You can stick to MD only if you are willing to see what happens and make improvements as a reapplicant if you are unsuccessful this cycle.
You have a very decent shot, but, despite your excellent GPA, you are not a slam dunk guaranteed A because of the MCATs. You are not URM or low SES, are you? If you are, that would change everything.
And yes, if your lowest FL was 515, I'd be disappointed too. What was your FL average? Maybe even consider another retake next year if you are not successful this cycle and you have good reason to believe you could hit 517+. That could absolutely make a difference, if necessary. If that's in the cards, and you don't really want DO, that would be a good reason NOT to apply DO this cycle. You just need to be careful not to rely on relatively high FL scores if they are from FLs that you used when preparing for your first exam, because those will be inflated since you saw the questions before, even if you don't consciously remember them.