I do not like the abortion shots for dogs because they predispose the dog to pyometra, a dangerous uterine infection that is often fatal. What you CAN do, though, is get the dog spayed up to 40 days gestation. This will abort the litter and will prevent future litters.
An average heat cycle lasts 21 days so it sounds like you are on the tail end of this one.
Let me know if you still have questions.
