Your identity is not defined by your external appearance ever.
There is no such thing as truth, but only perception. Why on earth would you allow someone else to define YOUR reality?
I was mistaken for a boy quite often until I was about 16/17. I was chubby and my parents were poor so I wore my older brother's hand-me-down clothing often in addition to having really short hair because my mother was a bit older when she had us and just wasn't into the whole "girly girl" thing.
Ironically I grew to be a fitness/swimwear model.
