He's a young dog, working in a tight space...it's hard to keep his attention.
All the classes I've ever taken were outside or in big arenas...and what I've done if the dog got too focused on another dog...or too ansty and wanting to play...was just walk them out of the certain area...and do our work away from all of the commotion.
I think you will have better luck with an instructor that has working breeds. I would put the prong on him...he's big and he's strong now...and it's not worth you getting hurt because the dog takes you off your feet.
When Baxter was about 9 months old (around 90 lbs)...he thought it might be fun to lunge at passing cars when we were out for a walk on our country road. There was no way...that a martingale collar was enough for him ...or for me walking on an icy country road. I bought a prong collar....fitted it right...and a couple of good self corrections and he was good to go.
Never did it again. Never have used the prong again. I could have worked slowly on it with only positives...but I thought I might break a leg before he learned.
Things will get better...he's just starting his teen phase.
Gina