Last names

So my S/O and i have been together 4 1/2 years ! And we’re expecting our first baby girl in November, and we choose to allow the baby to have his last name. Now I’m getting shit from my parents about the baby needing to have MY last name because I’m not married yet. Me and my s/o plan to get married it’s already in the works so i don’t see the big issue. I just really don’t know what to do at this point rather allow the baby to have her fathers last name or obey my parents and give the baby mine ??? OPINIONS PLEASE