I'm not ready to be a MOM

I can still remember the first time Chance called me "mommy". I loved it and sounded so good to hear. But for some reason in the last few weeks Chance has taken to calling me mom. "thanks mom", "can I go outside mom", "good night mom". I'm not ready to be mom yet. I still want to be mommy! I tell him that he has to call me mommy untill he's 12! Maybe by then I might be ready to be a mom. Right now when he calls me mom I'll correct him and say mommy. (in a playfull manner - I don't get mad at him for calling me mom) But for some reason he is set on me being "my mom" (as he likes to refer to me as).