Press "Play" to play the game. (There might be a time when the crystal just keeps bouncing in the same directions. Just re-do the game. It should work.) Also, about the backrounds, if you click, "galaxy", it will stay the same. If you want to change the backround back to nebula, you will have to re-start the game.
Also, I want to add music to it but dont know how. Can anyone help me? If you have on the galaxy backround, then there might be a few glitches when you press back or start the game, and the game-over page will not be shown. For better quality, I recommend keeping on the Nebula backdrop. I might sometime add a shop.