Demigirl is a gender, someone who is demigirl could identify as female or a female aligned gender and a androgynous/non gender like Non-binary or agender. Or if you want the Google definition; A gender identity term for someone who was assigned female at birth bus does not fully identify with being a women, socially or mentally.
That's ok :)
I'm only a year older but I started when I was 10-11 and I had the same thoughts but it really doesn't matter on here, everyone is accepting ^^