I resently began riding again ( I had my second lesson saturday) and I began canterering on a horse, Paco. He was fine going left, but I when we went right, he stayed in the left lead. Im not really sure how to fix this,
Does he know flying changes? If you're cantering around on the left lead and suddenly turn right, unless he know's lead changes he's going to stay on the left lead, or disunite. If you're lucky he'll feel unbalanced and give you a clean change. If you are just doing basic flat work, when you change rein in canter, just bring the horse back to trot for a few strides, change bend and flexion, and ask for the correct canter lead.
How much experience do you have? And what does your trainer say?
We have a few beginner school horses that are older and a little stiff to one direction or another. For someone who's only cantered once or twice I don't worry about them picking up the correct lead (unless that horse is really uncomfortable on the wrong lead), I just want them to get used to the motion and start getting secure at the canter. Once they've cantered at least a handful of times I just have them go back to a trot and then try again. 9 times out of 10 it's because they didn't ask clearly, but often it's conjoined with the horse being stiffer to that direction.