I'm still very confused about what "being a girl" means...
At what point is someone "really a girl"? What is the checklist to know that you are girl or not?
For me, I have a lot of trouble saying anything about me being "really a girl". I can't say I'm a "girl trapped in a mans body", because, I don't know if that is true.
I don't really have an answer

Is it the desire to want a feminine body? Is simply wanting to start hormones the defining factor? I'm not sure, it doesn't seem enough to dictate "being a girl" or not (my sister tells me all the time that she doesn't like being a girl, but she still is).
Is it how you talk? Or what you like? These are all social things (sure there might be some general things one gender leans to over another, but it is not even close to absolute and it is more about social stereotypes and man-made things like that). I can't say that I am a girl because I liked tea sets when I was 7... it simply doesn't work that way.
So, I don't know

I want a feminine body, I like the changes and effects of hormones, I have a lot in common with "girls"... but, I simply can't say that I am "really a girl". I have a lot easier time just saying I am "Trans", whatever that means.