You're doing well already! Deciding to ride again is a big step.
I had a bad fall and hurt my back. No surgery, no serious injuries, but I was nine years old, so... yeah. When I go back on my pony, a total sane, grumpy old horse named Melvin, I was shaking and sobbing the whole time. Now, two years later, I'm training horses and jumping 2'6. So, eventually, you will get back in the swing of things, but be patiant with yourself.
Only ride at gaits you feel comfortable at. If you don't want to canter, or maybe even trot just yet, don't. Eventually you'll feel confident enough to do everything you used to, but it will take time!