With only two years, and being self taught, it's possible that you are not as secure in your own balance on the horse, too. So, you might be leaning forward when you ask for the canter, and thus the horse gets a bit off balance, and she then rushes forward to try to recover balance, which causes you to lose balance and curl up forward. It's a vicious circle. How do I know? Well, it's something I dont' do as bad as I used to , but I sure had my time doing that every time I asked for a canter
There are just loads of threads on here about canter departs and how to make it successful. I gotta get cookin' right now but if you scanned around you'd find some real gems.