so im soo close to getting my heelflips. the only problem is the board always lands directly behind me. if it was only a little more under me i would have it. so what am i doing that causes it to land behind me?

Don't lean over the board so much. Stand up straighter when you go to pop the trick. Thats normally the reason why the board lands behind people.

keep good posture and keep your back straight
it would also help to put your foot directly square on the tail, not in the corner pocket like some other people

kick straight out in front of you
it keeps the board under you

keep your body straight