I'm going to lie to my girlfriend and not wait for her to get out of class
Why can't you just tell her after school? And why do you need to lie?
I'm tired of waiting for her to get out of class
Relationship have a lot of give and take. It's inconsiderate not to wait for your girlfriend to get out of class.
I want to see if I can get away with it.
Whatever you're going to say to her, I hope that it will be true and you shouldn't experiment on her to see if you can get away with lying to her as she could feel very hurt if you do so. If she found out that you are lying then she might break up with you and you may not like the result in the end.