I finally told my mom I am Atheist!?

I took the advice of some of the people here on Y! Answers...It didnt go over so well. Mom was sort of tweeked when her sixteen year old son mentioned Atheism and now if I try to talk to her she tries to coax God into it somehow. It seems like all I do is argue with my mother about religion now and I don't want to argue! She can be Christian that's fine with me, but I do not want to be, that's that. Why does she resent me now? Did I make a bad choice and should I stop looking at things so rationally and go back to church and keep my mouth shut?