pffftt I'm scared!!!! lol Cantering my lesson horse, excites her a lot. Especially down the long end of the arena. She's a spunky girl, and I get scared with my corners.
I would ask maybe if your coach has someone else even if it's just for a lesson or two that's slower to help with your confidence. With the other horse I ride, he's got a super nice canter. We cantered for 30 minutes, I've never done more then a minute on my other girl. He's got a nice canter, I can relax my breathing and think! and not worry about anything else.