I will certainly concede that TERF gets over used, and often used to describe people who are not actually TERFs. If you are not actually a radical feminists, then TERF doesn’t actually describe you. By your own words, though, it’s obvious you are anti-trans. Your rationale: that there are only two sexes, that transgender women are men who are somehow gaming the system, is certainly reminiscent of forms of radical feminism that believes that gender is a construct used by men to subjugate women and that women are only subject to misogyny based on their reproductive abilities. If you agree with that ideology, you can probably see why you might be mistaken as being from a particularly reactionary and fundamentalist branch of radical feminism. Please forgive the error.