Things I learned:
1) when cantering, the inside leg is the gas and the outside leg goes back
2) Gem really falls on the left shoulder - is he favoring a leg?
3) my legs need to be further back and my thighs should open more
4) no neck bending in dressage really
5) Use my inside leg to keep him cantering
6) transition down by straightening my lower back (essentially, stop riding - but a different slant than I've used in the past)