Dominick I have to say that I think you passed perfectly visually pre-T (I have no way of knowing whether your voice passed, lol), and T has only enhanced your masculinity. I'm slightly envious, lol.
I'm so sorry you got mis-gendered. I can only think of two reasons why it might've happened:
Firstly, unless they're Sherlock Holmes, people very rarely look at people properly on first meeting. Particularly when there's only a brief or cursory interaction, people often take in other people peripherally or just at a glance. You might be the most masculine male that ever did masculine, but if someone clocks you out of the corner of their eye, they can miss all of the indicators that say you're a man and make a mistake, particularly if they're working on a till and deal with a stream of customers in quick succession - I know when I swipe folks' membership cards through at work, everything gets mixed up, lol - after an hour of people whizzing past, repeating the same interaction, I don't know what's male, female, up, down, red, blue or green. A panda could probably walk past, hand me its membership card and I'd mis-identify it as a marmoset.
Add to this the fact that gender ambiguity is becoming more and more commonplace and I think that lots of people find it increasingly hard to read conventional gender traits as signifying the gender they're associated with. Oh Dear. That makes no sense. I mean... Aaargh. How can I express this? It's no longer universally true that a person with a deep voice, masculine features, a short haircut and masculine mannerisms is necessarily a man. I think people are becoming more aware of this, and it's creating some confusion, particularly (though I don't want to generalise) for certain members of the older generation who are used to more rigid and unambiguous gender roles.
An older female customer walked into the bingo the other day, handed me her card and said, 'There you go, Son. I mean Darling.' Then she stopped, looked at me intently for several long moments, seemed to give up, and said 'You just can't tell nowadays, can you?'
All of this of course doesn't make it feel any more wrong or frustrating when someone mis-genders you. But hopefully it might provide some explanation for an otherwise inexplicable occurrence - because you don't look remotely female. You're all man, mate. *Seethes in quiet envy*