How do I know?
If you had asked me a year ago what my gender identity was, my answer would have been rather different than if you asked me now. I tend to be skeptical that I have the appropriate epistemic vantage point to have a certain answer to such a question. I'm not even sure there is such a thing as a persistent, innate, or essential gender identity.
Philosophical problems aside, assuming this is a census or something, I would be considered a trans woman.