Leg on leg on leg on. Is what I am told by my instructor if shes lazy you need to carry a crop with you and tap her and use your leg preasure to get her moving. I ride lazy horses to and well its hard at first but it will eventually get to where they know they can't be lazy. Its all about body,legs,and hands. Kitten_Val Is right your post is a bit high and you use your legs to post. It also looks like your leg is swinging quit a bit. I can't reall tell though. Its only your 7th lesson you will get better and better at each lesson. And being on the wrong diagonal means you need to ride the wall and look at the outside shoulder eventually you will get so used to it that you will be able to get on the correct one right away.
anyway good job and keep working at it you will eventually get to the point where you will have the correct idea of riding english :) everyone goes through it.