I started riding about 11 years ago. It took me a while to get more comfortable around them. And learning to canter took quite a while! The arena we had to ride in was a bit small, so I felt like I would fall off when we had to turn at the corner of the arena when trying to learn to canter. Then one day when my 4-H group was at the fair, I was in one of those horseback game events, and I had to canter back, across a long long arena, and it just clicked. I think because I had a long distance to be able to canter in a straight line, and I was able to find the right position to sit and keep my balance.
Take deep breaths, and when cantering, you want to be leaning slightly back. I used to end up leaning forward when trying to canter, which throws you off balance and makes your legs rise up.
Lean a little back and stretch your legs down into your stirrups before you start to canter.
Just keep working at it!! Good luck!!!