Button problem on down state with tween

Hi all,
I have designed a short quiz and when the user clicks on the correct answer (button) a balloon is meant to float up across the stage. The problem is that the balloon only shows briefly when the button is clicked - and can only be seen floating up if the button is held down. What AS can I use to correct this and allow the viewer to see the full tween without having to hold the button down?!

Thanks