I can relate, too. I am passing without question to some people I have known for years (yay internet) at first it didn't matter to me but now that we are friends and we do have video conversations, I feel like quite the lair because I'm not what they perceive me to be. In many of these cases, I will come out in time. In others cases, I won't, because they are people who matter less.
My advice to handling this for you, since to me it seems to be more of an issue people you meet casually, is to know they see you exactly how it "should be" if not "what it is" and if they really and truly matter, you'll tell them the truth in time. Random people do not go up to other random people and say "Hi, I'm Bob, and I am 30" or "I'm Maddie, and I have six toes" even if the public assumes Maddie has five toes and Bob is actually 23. Neither is lying by not saying these things - people just have preconceptions about people. If you want to shatter them or alter them, go ahead. Most of the time, though, there isn't a need to go up to people and announce that you might have six toes.