who doesn’t want to be 100% a man or 100% a woman.

I’d go further and avoid any kind of “want to be” wording in explanations to people who can be really doubtful. Gender is who you are, not who you want to be. If you tell them “I want to be <other gender>”, they might form some kind of “attack helicopter” opinion/joke. but if you tell them “I’m <gender> on the inside” or “despite my body, I’m actually <gender>”, that leaves a lot less room for wrong interpretations.

“Someone who’s gender identity neither aligns completely with man or woman” would be my rewording, in this case.