Really confused on what to do help

Im almost 23 weeks and throughout my whole pregnancy the baby’s dad hasn’t been there im blocked on everything and we haven’t talked about anything AND he’s denying she’s even his,he has a new gf now😭 im just not sure what to do should I give the baby his last name? is he going to be on the birth certificate? I doubt he’ll be there when I give birth I’m just confused on everything if anyone went through something similar or if anyone has any advice please share!!