Do I have a right to be a bit annoyed?

Okay so I’m a stepmom to my partners 7 year old son. We also have a 4 month old daughter together. Obviously I’m known as my first name to my stepson but my partner keeps referring to me as my first name to my daughter.

I know he isn’t doing it on purpose and he doesn’t realise he’s doing it but when I say to him that he didn’t call me Mommy to her, he says I’m overreacting and should just leave it.

I’m already aware that she may probably call me by my first name at some point after hearing her brother do it so much but I don’t think it’s a mistake my partner should make.