D/S means duration of status so as soon as your program was over your status expires and you have 60 days to leave (grace period). That the visa is valid until 2016 is not relevant in this case. You have not accrued unlawful presence until a judge has made such determination. I don't know what you mean by "cancel." You should take your DSO's advice. By remaining in the U.S. you are not changing anything.