those situations are always very awkward and anxiety-provoking. i hope you're feeling better soon.
occurrences like this have happened to me, and although i can recall them clearly, no one else involved remembers them. so honestly, he'll probably forget about it soon enough. most people do.
on the off chance he doesn't forget and confronts you (and you're not ready to come out), you could possibly say that you're doing some research for a friend who is questioning their gender identity. but if you are prepared to come out, and the if opportunity arises, don't give up the chance; you may as well tell him.
however, he's most likely going to forget about it, so there's really no reason to worry. but either way, we're all here for support.
hope all goes well,
jackson 🙂