I am not a rider either but I have been a horse mom/grandma for twenty years. Currently we are having similar issues with one of the horses. A few things come to mind that we use and seem to be working. When you warm up start slow. Walk in hand for a few minutes and then get on. If you can, find space to do more walking and stretching, then progress to easy serpentines and circles, and finally the trot. He does not get to canter until you allow it. Try not to have a death grip on the reins–give him his head space. He may also be picking up on your excitement and is responding to that. Reward immediately for good behavior with a simple pat or “good boy”. We are in the process of “deprogramming” a former barrel racer. She thinks the arena is for running too! I know this is all basic stuff but it is working for us and also worked for our 4 year old OTTB. Good luck!