Amanda Serrano's issuing a mea culpa after accusing Katie Taylor of intentionally headbutting her repeatedly ... taking to X to tell everyone she was way out of line with her previous comments.
Here's the deal ... Amanda and Katie brawled just before Jake Paul took on Mike Tyson down in Dallas Friday night -- and, during the fight -- Katie's forehead came up and smacked Amanda right above the eye.
Taylor won the fight by unanimous decision .