A rumor about you only grows if you keep watering it with reactions.

A story about you needs your reaction to stay interesting. Every denial, every angry message, every time you raise it gives the thing another day of life and one more detail for people to pass along. Ignoring it is not pretending everything is fine. It is refusing to be the part that keeps it running.

Tell the few people who matter the real version once, calmly, then stop, and say nothing in public. Most of it dies of boredom within a week or two. If it turns into something serious, that is when an adult or the school gets involved, not a reply.