I talked behind my ex-friend’s back and she slapped me—how do I apologize now?

I made a huge mistake and don't know how to deal with it. I took karate for 5 years and Im goinginto junior year at University. I had a bestie (sort of) at the beginning college. As time went on, tbh, jealousy started setting in. she's sort of the blonde Barbie type, gets a lot of attention. We drifted apart and I started talking behind her back. We recently got into a confrontation. She knows about my having taken karate. We had a confrontation last weekend. After verbally going back and forth, I moved forwards towards her and she backed up, looking behind her. She looked unsure, a little worried. But she backed against a railing and couldnt back up any further. She changed her disposition and off handedly said “Awgh, I never believed any of that karate crap anyway. I easily got every fuckboy and you're no different. She smirked. She'd had her right arm dangling down and all of it a sudden it flung to the outside. A slap. But she was way too fast for me smh. Her right smack came all the way around and slapped the crap out of me fast! I was shocked as my face spun but a second later the sting set in and I yelled OWWW! She just smirked at me as I cringed and went uggh! I never thought that could happen to me tbh. She was right. But now Im completely humiliated and frustrated. Should I apologize to her? If so, say what exactly?
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I talked behind my ex-friend’s back and she slapped me—how do I apologize now?
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