First of all, being drunk is never an excuse for physically lashing out at another person. Your girlfriend exercised very poor self-control in both saying hurtful things and in hitting you. Her behavior was abusive and unacceptable, and there's no need for you to apologize for her bad feelings. She's capable of and should be responsible for dealing with her own emotions. It is not your job to make her feel better. You have set a boundary with her and if she can't respect your boundaries then she is not someone you should be with.

If you don't want to have sex, you should not push yourself to have sex. It's your body and your choice, and it's important your partner is able to accept that. If your partner can't accept that then maybe it's not a good fit.

I would suggest talking to your girlfriend when you are both sober and in a good headspace. Let her know that her actions hurt you, and that they weren't okay. Explain to her that you have been honest with her and that while it's not a reflection on her or her attractiveness you choose not to have sex for personal reasons. Ask her if there is a way you can validate your love and attractiveness for her without crossing the boundary of sexual contact. Try and come up with a way to do that together. If your girlfriend insists it HAS to be sex, then I would say it's not the best relationship for you to be in. Relationships are about respecting boundaries, and if someone can't do that they aren't the person for you.