Try to focus on pushing your heels down and using the sole of your feet to absorb the motion, like a spunge. I really love how you didn't brace on the horses mouth, like mentioned above. That is one of the biggest things with new riders.
Try and flow with the horses motion, instead or against it. Really relax and try to be nice and soft instead of bracing for the movement and getting that really strange 'bouncy' feeling. Once you canter for a bit longer, I garauntee you will look like you've been doing it for years. Good job!