For the rope placement, make sure you can see your hands and that they are close to your body and slightly out front. If your hands are way out to the side, the rope will become higher to jump over and potentially impossible to make.
The jump should be the same as progression 1, relaxed and easy on the balls of the feet with a strong midline.
Next, focus on keeping the shoulders back but the upper body and arms relaxed. “Relax your face” is a good cue.
To spin the rope double time, practice a flick of the wrist versus the whole arm twirl – like shaking their hands dry – while keeping elbows in towards the body rather than out to the side.
Homework: Even the single under is challenging for many so until you are a single-under ninja, you shouldn’t be moving on to attempt the double – the neurological component isn’t there yet. Continue working here on the single before moving on.