Help?! Needle in dance?

-I am flexible enough to do a needle in dance (when you have one foot on the floor along with your hands and the other leg is straight in the air , so your body forms a straight line)... I know i am flexible enough because i am able to do the needle against a wall . But when i try it without a wall i am unable to do it. I think it may be because i am not strong enough in my legs. So does anyone know what the reason might be, and if it is strength some exercises i can do to build the muscle that i need?

Thanks :)