It’s true, mistakes will happen! I think the key questions are:
- are you clearly making an effort,
- when you slip up, do you apologize (but quickly, without making it all about you and your heroic efforts gone awry), and
- do you take ownership — adopting the attitude that this is something you need to learn, rather than a burdensome problem being imposed upon you?
If you’re 3/3 — and it sounds like you are — then no worries.
Although I do think it’s worth noting that the “premarriage name/postmarriage name” comparison is imperfect, since many people who change their names for marriage are completely fine with references to their previous name (myself included). By contrast, deadnaming — calling someone by their former name that’s misaligned with their gender — can be very hurtful and upsetting for those on the receiving end, so it’s not something that can necessarily be shrugged off no matter how well-intentioned the perpetrator might be.