Well, first off welcome to the forum! And welcome back to riding!
Don't feel too bad, it takes the average person some time to get the rythm and feel of the canter down. It might be that the horse you are riding has a particularly hard to follow canter. It differs a lot from horse to horse.
I am spoiled in that respect, as Mac has the nicest, easiest canter inthe world to ride. And that has helped me a lot to be more comfortable at the canter; riding an easy to canter horse.
As for things to do at home, hm m m . I suppose anything that helps to strengthen your core muscles.
Some people say that riding on a swing is somewhat like cantering, you know, the action of "pumping".
I think I'd just relax and try to realized that it just takes time. Rest easy knowing that you are going down the same path everyone does, and you might fall off a few times on the way. I still do!