Awkward situations

Broke up with my baby's father not too long ago, I'm 15+4 right now and just found out I'm going to have a son.  I don't want the fathers name on his birth certificate, since I know he'll just make things more difficult. I'm fine with him seeing our son, but I don't want him having some claim over the child when I know he's never even wanted kids. Anyway at this point he's saying he wants to go my ultrasounds and things, but I don't want him there. He didn't know about today's appointment and I have yet to tell him that I know the gender but I don't know how to do it without him starting a fight. If you have advice I'd love it please. Thanks.