Same thing happened to me. Always used my father's last name. HOWEVER, I love my mother's last name and I'm happy it's now "legally" my last name. If you go to college, just change your name with student records!! But you really don't have to. But all your legal documents should have your mother's last name.

I actually want to eliminate my father's last name. When I was getting my SSC, I asked the lady attending me about it, and she said when I get my permanent residency or citizenship (I think it was the latter), she said I can change my name to whatever I want. So there you have it.