My father remarried after my mother died then he died. Is his surviving widow still my step mother?:(

Till the time a person don't legally divorce his wife, she remains his wife, even if he died. So in your case, as your father has died, his wife will remain your step mother, because she has not been legally divorced by your father in his life time.

I think that is a personal decision between you and the "step mother". If you two want to keep that relationship, then yes, but if you don't, then no.

If you are under age though, it maybe up to a court to decided?

My father remarried after my mother died then he died. Is his surviving widow still my step mother?:(
If you have built a relationship with her then its for you to determine if you want to commit to that relationship or she will be just your dad widow