Girly username? "Alicorn" strikes me as pretty gender-neutral. The first mental image that popped into my mind before I learned about your gender, ironically, was a male, although not decidedly masculine, fantasy elf.

But yes, invisibility is a common problem online. I don't myself assign any prior probabilities to any given person online being a certain gender, unless the community is explicitly designated, for example, as "meant for women". But many communicate from a "male as default" standpoint, and maybe the only real way to combat it is to balance the gender ratio to a critical mass at which point that kind of prior simply becomes useless.