I had a similar problem when I was learning how to kickflip and most of it is in your head. Some people say you can practice kickflips on carpet, grass, or anything to prevent you from rolling which I tried and didn't really help much so I practiced in a hockey rink and smooth wide open places like parking lots. What you're going to try to do is place your backfoot on the tail of the board with your heel hanging off and have your front foot behind the front bolts facing a little towards them
You are going to pop as if you are going to ollie and set it up as if you are by dragging your foot straight up in order to keep the board under you and lift your back leg so that while the backs floating up you can flick out when you reach the concave. Watch the board and plant your feet when you see
the grip. Hope this helps.