I don't think u need to notify anyone.....AP is a way for u to re-enter if you leave the country while in AOS.......if u cancel ur plans, there is no need to use AP...it will just expire whenever on it's expiration date.....until u hreach that expiration date, u still have the option to leave and get back to the US.
Lifeonhold
I am not a lawyer...please treat this just an opinion!!