He must feel and know how easily he can make you feel worried because from the post he was a punk during the canter section of your lesson and he had no reason to refuse and did because he knew he could get away with it. I didn't mention him being a turd by trying to roll while you were on him??
You can do it! It looks like you're a decent little rider so don't let him push you around and be firm with him. You need to correct this or it's going to get worst and he's going to continue doing more and more bad things with you and you don't want that.
Hehe... I guess he does know he can kinda take advantage of me. It took me completely by surprise when he refused because his ears were pricked and he had a nice springy trot and looked like he was going to jump it. I'm definitely going to need to be firmer with him. >.<
Every ride, good or bad, teaches you something new.