You are incorrect. In intersex cases it may be more difficult than usual to identify the sex of the individual from a casual observation. However they still necessarily only have one sex: they produce either male gametes in which case they are male, or they produce female gametes in which case they are female. Even intersex people do not produce both gametes, therefore they are either one or the other. Therefore all humans fit neatly into either male or female biological sex, whether that sex is obvious from a casual observation or not.
As I said, it is important to respect individuals' religious beliefs such as gender identity as long as those beliefs are not imposed on others, especially children who do not yet have the critical analysis skills to make their own informed judgments.