I am not a fan of the "arched" back. It causes a rider to lock up and be stiff. I would much rather see a flatter, more relaxed back.
You need to bring your shoulders back and drop your hands to the side of the horse's crest, not on top of the crest. If the horse needs to stretch down or out, planting your hands on top of the crest will make you unable to give with your hands and give any rein.
I would also like you to relax your lower leg and wrap it more around your horse's barrel. That will make your lower leg much more secure when you start jumping larger fences.
I am being very nit-picky here. All in all, you are doing well!!