Originally when I did an app for a job, the gender was optional but after my interview I have to do a form and it has gender as required. I'm not sure if it's illegal to put female or not... I just don't want to put male. I can pass for either gender right now since I get called she sometimes, but I havent started hrt yet. If anyone could help, I'd be very thankful.

Are they hiring you?

Likely, yes.

What to put down depends on the laws of where you live and what they are going to do with the information. If they are going to run a security check or need it for Social Security records, it needs to be as it appears in your legal records or you may lose the job. The option alway exist to ask the HR office but you may be outing yourself to do so.

I understand and thank you.  ^^

Laws where you live... Interesting idea. If you can't discriminate on gender id, then you could put F if your birth certificate says M.  I don't thonk I have ever seen a 'We hire without regard to gender id' statement tho.