What everyone else said!
That sounds like a maya - the up and out and down vertical 8. We learnt with heels coming off the ground to help the hip go up, which some teachers disagree with. I think this is because you can "cheat" on the hip up by pushing with your leg, rather than generating the movement from the muscles round the hips and sides. Flat-footed you are forced to work those muscles more, and eventually it's much smoother and more self-contained as your feet don't have to join in.
I can't speak for anyone else, but on me I can sort of cheat the "up" using the leg, but not the "out" - that has to come from the hips. If you are generating the first part a lot in your legs then maybe that's why you get stuck at the hip out.
Practising sloooow hip slides might help you get the feel for stretching your hip out to the side. Also remember your hips are linked together - you physically cannot slide one way out to the side without the other coming along for the ride!
It just takes time and practise, and lots of different explanations that make no sense until you find the one that clicks for you. Good luck!