you aren't doing so badly. the mare is very downhill in build, and she isn't very energetic in her trot, so it's harder to post off her. you do better at the canter, but you must raise your hands. keeping them down so low is a habit I see in a lot of WP riders, but it makes it impossible to have meaningful contact. I know you are not at that place yet, but it will help your seat too, to left them up, let your arm hang down alongside your ribcage, put a bit of bend in your elbow, and aim your thumbs at her bit, so theire's a line from elbow, thought hand/thumb to bit. look up, too.
it'll get there, don't worry.
oh, it's hard to see, but your stirrup might be a tad long.