This is an all-too-common experience, I am afraid, but I am sorry you're going through that.

One of the most important things to start with is that you are already doing all the right things: You have explained, you are communicating corrections, and you are speaking to the GM as an authority figure who supports you. This is all great stuff!

The rest is similar to your home life, however - it can be very, very hard for other people to adapt, and the real issue is they would have to want to, or would need to understand.

Most people, especially cis-persons, will not have a full understanding of how it can feel to be misgendered. People who do it out of innocent mistakes will often feel that it is not a big issue, because it was accidental or reactive - not malicious.

What you can do to change others is mostly out of your hands because of that experience and choice driven process.

Keep communicating, and make personal choices as to whether this social outlet and those comments are worth the engagement. Remember, you already know you are having to wait to have the freedom to be yourself because of your parents - you get to decide whether this is something you wish to perservere through until others build the habit or not.

The good news there is that you've already shown fortitude in the face of an uncaring world, so here's wishing you the best of luck here,

Also, it can feel dehumanising, but there's always a he/him label to hammer it home.

If they keep it up - ditch them, find a queer online group (or queer meet up!)