That use to happen to me all u got to do is commit it is easier to do it moving if u have that problem also try jumping forward at bit but also try to keep it under you

just jump higher and forward and bend your knees :)

Just pull which ever knee is doing the pop up after popping. In other words just bend your back knee after you pop

Skating can really get to your head, if you feel uncomfortable or scared you can try it in the grass or somewhere the board cant move, jump up higher and get that back foot on. Bend those knees