I'm kind of mad that my gf doesn't want to go watch a movie together
Why doesn't she want to go watch a movie with you?
She has some kind of excuse about why she needs to stay home.
If she does not want to go to the movies, you need to respect that. Maybe you can meet in the middle and you both can watch a movie at her place.
Nah, I want to go out.
It's fine if you want to go out to see a movie, but you can't make your girlfriend go with you. There's nothing wrong with going to the movies alone.