Your hands look good. try to keep your toes forward, not out. and try not to let him (I know, it might be hard, because hes a reiner) lean in on the corners, and maybe (I cant really see what kind of bit you have very well....) try to have more contact (Will he take it? it might be easier to maybe find an english horse? because a lot of dressage is aids and the rein contact and effectiveness of the seat and stuff.)
But overall it looks good :) oh, and close your hands more (that does NOT mean have a stronger stiff contact or anything, it means tightneing your hands, not your contact) and put your shoulders back in a soft relaxed way, dont brace, that always looks bad and makes your seat in-effective.
But its good overall :)
If there are no horses in heaven... im not going.