Birth certificate

Cheyenna

My due date is 4 weeks away and I’m still not sure what to put my babys last name as. I’m engaged but not married and I feel pressured by his family to put his last name but I don’t want the baby to have a different last name then me. I’m kind of scared to get married right away just bc of how pushy and controlling his parents are. What do you suggest I do? Is it hard to get a birth certificate changed if we do get married???