Our latest library trip

So we go the library. I don't think David knows what he's agreeing to when he says Yes, but because he agrees, we go. (This is for story time at the library.) "Will you sit still?" Yes. He sat for 2 minutes, then was playing again. I got so mad. Finally I took him back to the car and really yelled at him because he wouldn't sit still! He did not take it well. But when we got home, he sat still and we read four books! It looks like I'm going to have to really start to get stricter with him if I want any results. He can't continue like this. It won't work for his future!