Ugh, I feel so dumb!

I bought this really cute return address stamp for my mom and her husband (they're obsessed with foxes) off etsy. But I totally messed up and put Carters when their last name is Carter. The example stamp the shop used had Collins, which is an actual last name and I just wasn't thinking. Is this completely bad grammar or is it just not the preferred way. To me, if it's going to be plural it should say "The" in front of the name.

I was thinking I could just ask my mom if she was ok with it this way but knowing her she would say it was fine and then only use the stamp on envelopes being sent to me.