You really haven't thought this thru have you?  In order to claim that you're a girl you'd have to live as a girl full time 24/7.  Makeup, hair, clothes, the whole bit.  No boys sports.  No hanging with the guys (that's assuming that your former "friends" would have anything to do with "the chick with a dick").  Of course you'd also have to live with the continual risk of assault (physical and/or sexual) by people that didn't approve of your very existence.  And that's not to mention that you just took yourself completely out of the hetero dating pool.

And all that for washroom access.