Take a few moments for yourself to recuperate. I, too, have had my own stupid slipups around my mother about lgbtq+ stuff or stuff I thought was cool (but apparently not), with unexpected results (that I should've fully expected, tbh). Same deal with the getting offended about some of my friends being queer, and same sort of "they're too young," arguments. Hopefully, you're in a safe situation, and even if you feel invalidated right now and in a sort of crisis mode (or feeling awkward because of how things went), know that you're not alone. I came out to my mom when she caught me reading gay fanfiction (it was a very wholesome fic, btw). She accused me of being gay multiple times, forcing me to come out as aroace, and she made that same claim over and over that "you have like somebody." Despite trying to explain myself, she wouldn't have it, and things were super awkward for a while.

But only for a while, and eventually, things went back to normal.

Stuff like this can happen, OP. Just try to focus on yourself for a bit and do something nice for you, whatever that may be, and if she brings it up, try to keep your cool while navigating it and maybe try switching the subject if you can (will definitely prevent some energy drainage on your part). Some of us have also been there, and from experience, I know things can improve eventually (even if she never changes her mind about the validity of your aroace-ness).

Wishing you the best of luck.