I (42) have a step daughter 'Liz' (17) from my wife 'Kate' (42) first marriage. Me and Kate also have a daughter 'Emma' (3) together. Liz doesn't call me dad and usually refers to me as Mr my last name.
I'll be honest that this bothered me a little, but this is what Liz feels comfortable with so I never pushed it. We're not close, but we have a good relationship overall, and she loves Emma.
We weren't able to get together with my side of the family over Christmas, so my family had a late Christmas/New Year's gathering where my mom gave her Christmas gifts for the grandkids. She got Emma some toys and Liz a sketch pad (she's an artist so it's not a random gift).
Liz (and Kate, my wife) were disappointed, and Kate pulled my mom aside later (I was around) to say she shouldn't have given the gifts out in front of everyone and Liz is hurt.