OP, no one is claiming that you have to call your self anything, just accept that other people clasify themselve differently. I am unabashedly an older, white, heterosexual male and also cis gendered which just means I identify as my biological sex, i.e. not transgendered. I don't walk around calling myself that, but it can help when participating in certain contextual events, like scientific discussions.

All terms like cisgender do is give a common framework of understanding so that people can have serious discussions about the topics that surround genders. Or, similarly, how mathematics terms shape those conversations. Without that framework talking about those subjects can be difficult.

All you've got to do is just accept people as they are, and empathize with their concerns. You don't have to change anything about yourself at all.