I'm going to skip a show to watch Wreck-it Ralph
Why would you skip a show for Wreck-it-Ralph?
It's better than going to a show alone
Since you are by yourself and are not interested in attending the show alone, it is perfectly acceptable if you want to skip it as long as it won't affect anyone else. If watching Wreck-it Ralph is what you prefer, then you should go watch it.
I wanted to watch my show, the principle came and yelled at me for skipping the show.
It sounds like you were obligated to be at the show. It is not okay to skip something you are supposed to do just because you want to do something else more.