Last name ex husband

I have my ex husband last name I still didn't told this to my actual partner he thinks is my last name I always denied my real last name because I never had a father by my side and plus is an ugly ass last name that ruin part of my life when I went to School lots of kids made fun of me this may sound immature but thats the way I feel about it I was married for 4 years change all my papers to his last name until today my social everything has his last name the thing is that I'm pregnant now and I don't want my baby to have my ex husband last name I don't know How to tell my boyfriend And how can I fix this I want my moms last name only is that possible? My mom passed away 7 years ago can I still claim her last name