冤: injustice, wrong
枉: 弯曲,扭曲的意思,crooked
so 冤枉 means : 被曲解了,误会了,蒙冤了 , someone is accused because of something they thought he has done(and it's bad thing), but actually he didn't do it
我没冤枉你吧 : 意思是那些事确实是这个“你”做的. i didn't blame you wrong ,right?
this expression may commonly used by parents blaming kids for bad behaviors