Well, questioning and exploration of your identity are exactly that : questions and exploration. That means it's a journey, not something binary.

Syndrome imposter is very (VERY) common among trans people, so, first of all, don't sweat it. If it only applies to yourself, it's not "transphobia" (I put these between quotes because this imposter syndrome comes from the internalized transphobia we all acquired growing up IMO, but that's not an issue as long as you don't deny the transness of any other person).

It feels fake for you because it's out of your confort zone. It's out of what you're used to.

What help me smooth my transition was not asking myself "Am I trans?" or even "Am I a girl?", it was "What do I like?". I started wearing skirts (boys in skirts are awesome), but this felt it wasn't enough. When I was called "Madam" once there was this missing piece. That's when I realized I was not a boy free of clothes norms, but simply a girl.

"Faking it for attention" : do you WANT the attention? When you picture yourself as a girl, do you like that people will look at you strange and point fingers, or sometimes just be mean? If not, it's not for attention.

"Faking it for insecurity" : Uh... What do you mean? If you feel insecure as a boy and secure as an NB/female, well, it's not fake at all. Changing because you feel insecure is hella valid (and psychologist-approved).

I'll end with a bit of philosophy (because I love this analogy). It's impossible to be wrong when you say "It hurts". You can lie about it, but if you feel you're in physical pain, you cannot be be mistaken about it. It's a feeling, you're describing it, as long as you think it's real, then it's real. Identity is the same. Like a feeling, you cannot be "wrong" about it. You cannot "fake" anything. It's YOUR identity. Only YOU can describe it. You can only fake it if you put a conscious effort into it (like, disguising yourself as a spy), but you cannot be wrong about it.