But, LaughingCat, how do you know "when your gender isn't right"? - Is it a case of "I just do", or something like "Don't I always know myself better than anyone else"? Do you think people always know the truth about themselves better than others?
Of course people make mistakes about themselves. Some people think they're clever (when they're not); some (especially adolescents, ime) think themselves ugly (when they're not); some think they're fat (when they're not) ... and so on and so on.
Thing is, LaughingCat, I'm sure (I PROMISE you (!)) children who say they know their gender isn't right only think they know this. How can I be so sure? - Well, there actually is no such thing as a 'gender' possessed by a child in such a way as for such a child to be 'not right' in that way. And you can't know something that isn't true, can you? You can think you know it, but if it's not true you can't know it, can you?
So, again, how do you know you're not mistaken?
Do I "genuinely believe there is no such thing as a trans person"? Only in the same sense I genuinely believe there are no people of way below average BMI who are actually fat, or beautiful children who are actually ugly. Of course there are some people who believe themselves to be so-and-so or such-and-such. In that sense there are such people. But sometimes, with a bit of thought and common sense, we can work out they must be mistaken about what they think about themselves. No?
This is not to deny the existence of anorexia nervosa or body dysmorphia, is it? And ... well, fill in the rest.