what can i do to make my girlfriend happy?

it is a hard thing to say not knowing her one can only guess my guess would be think of something she really really likes something usually small maybe one would not notice but sometimes it is when another shows they notice the little things it is easier to remember why we do love the other she may still be mad but if you can bring a smile to her face your half way there think of something she really likes whether a back rub or maybe she hates the dishes or loves a certain kind of food but never gets it or never treats herself show her she is the queen and you may be once again a King

I guess you start with apologizing to her in person and admit all your fault to her, just be humble to say sorry. Then you can treat her in lunch and watch movie together. Be sure that both of you are in good terms.