Lope = canter and vice versa.
I've said canter when I meant lope. I "lope" my reiner off, but she's technically "cantering"
Reiners never actually truly gallop. Most horses don't truly gallop that often.
OP like someone mentioned he probably just needs a refresher.
If he goes to fast, stop-back-roll back and go off the other way.
Do lots of lateral and bending exercises to get his body working the right way. Expect him to lope off slow, if he "canters" off then you may need to stop-back-roll back and continue.