the quality of the video makes it very hard to see much detail. It appears you are gripping up a lot, though. Your horse is "insulted" by it, and so has a swish to his tail and ears back. You are trying to stay on by gripping, and your legs come up , knees to far forwad, and heels up and gouging into his rib cage. And you are leaning forward.
Are these things wrong? Yes. Are they typical of first time canters?> YES!
So, you just canter more and relax as much as you can. It will get easier and easier and you'll be able to drop your legs down and ride by sitting down on the horse more. Good luck!