I am 12 years old and having problems with the Heelflip.?

Ok i know how to ollie, I have the rotation down for the heelflip there is only two problems,#1.When i do the rotation my tail of my board does not go off the ground.Problem 2 is that it seems that when i jump only one foot seems to land on the board (in other words am i not jumping high enough or accurate enough)???????please help me guys i need it, Answer to both questions if you can.