I don't really want to do this. I'm not qualified in either biology or psychology. However I also don't believe in simplistic models.
Our bodies and our minds are so inextricably tied together that attempting to say categorically "it's a choice" or "you're born with it" are both probably wrong statements. I would feel confident in saying that most people with "normal" /physical/ development have a pre-disposition toward the opposite sex. But also that life experiences, and brain chemistry anomalies (etc), can certainly change that outcome. As no doubt can mental disorders. Maybe even drugs. Or pollutants! Are the mental disorders in part caused by physical anomalies? Could be! Impossible for me to say.
In the vast majority of cases, I'd say that being born a woman with a healthy female body, hormones, brain chemistry (etc) makes you a woman.
I would, however, not select a partner from a genetic female who identified as a male. Neither would I ever select a partner who had been born a male.