First of all, you don't have enough strength in your lower back, or you're not using enough strength, you not only have to lift your legs up, but you also have to lift your upper body up, and only land on your back from your elbows

When you hit, your legs move, but your upper body doesn't move (and the reason you can hit it is because you're rolling your upper body down with your legs)

There's also the possibility that you're not using the right amount of strength in your legs, or not enough strength, and you're leg must be angled upwards, with 60% upward force. You have to hit your leg diagonally upwards with 60% upward force, bend your knee before you hit the ground and try to kick your butt with your heel, this will help you to get up, and the fact that it hurts a lot proves that you've practiced it a lot, so if you work that hard, you should get up in no time, check out the videos more often