I don't have any.. specific advice, but I do have a story that relates to this & can probably help.
Two years ago, I was riding a very advanced horse my first week cantering. The first time another girl let me ride her horse while we cantered, so I didn't have to canter him. The rest of the week, I tried on my horse. He was stubborn and would NOT go. The last day of the week my instructor fallowed him and got him canteirng. Being the beginner I was, I fell right off.
My confidence wasn't messed with; I was okay with it. It'd just been too hard and I'd known I was going to fall.
For some reason, my instructor asked me to ride him again the next week. I was the only one riding him at all, and he was very hyper the first day. Going over some poles, he reared and off I went.
I switched horses and was fine for the rest of the week, but I didn't canter.
I switched onto a very smooth pony the next week and was excited to try and canter again. We were doing amazing until that Wednesday, another girl tried to pass me and our ponies raced. Mine got too excited and I fell. After that, I was done. No more cantering for me.
It was only the third week of the Summer, but I didn't canter again at all. For a while after that, I was terrified of cantering.
One day in a lesson, my instructor forced me to canter and though I was scared, I put up with it. I was too scared to realize how much I actually liked it and didn't canter again.
I began riding another horse, whom I stayed on for months and months. I trusted him so much and after I while, I decided to let him "take off" with me and cantered a few strides. The next week, I was begging to try it. We were whizzing around the ring by the end of the day- now cantering was all I wanted to do.
I had a few falls after that, but I knew I'd want to do it eventually so I kept getting back on. (: