If you are trying your level best to present as a female and someone is deliberately treating you as a male, they are being RUDE. They are either nasty souls or ignorant.
I'd treat them as the latter, and make an effort to educate them. First assume it's a mistake (unless it obviously isn't) and politely correct them. "Oh, you're mistaken. I'm a woman. My name is Tessa..."
If it becomes clear it's deliberate, I would still try to educate them.
(Prepare for a cascade of post replies about how people like that can't be educated. I don't agree. Of course they'll never be educated if we don't try, and if trans folks don't educate people, no one will.)
"Don't you think it's impolite to treat a woman as if she is a man?"
"If someone clearly wants to be treated as a woman, isn't it unkind to do otherwise?"
"If someone treated you like a <whatever is the opposite of what they are>, how would it feel to you? Well that's how I feel."
or
"Treating someone unkindly will not get them to change gender. It will only make them feel bad."
The key is to get them realizing that we're human beings and that we are entitled to the same decency as everyone else.
Of course if they're just nasty sorts, you're better off walking away. No witticisms or quips will touch them. But I like to give people the benefit of the doubt.
