My girlfriend talked me into going to class with her and I regret going.
So you went to your girlfriend's class? Isn't that class boring for you?
Yes, and I'm not talking to my girlfriend after the class anymore
While getting into disagreements with your partner is unavoidable, you shouldn't stop talking with your partner if you are upset with them. Giving your partner the silent treatment does nothing to resolve the issue and can emotionally affect your partner. Rather than keep silent, talk with your partner to address the issue that has come up and try to resolve it as best that you can.
I already did.
I'm so glad that you decided to just talk things through. That's much easier than trying to use the silent treatment.