How do I quit the game?

I downloaded this app onto my Kindle Fire. The other 2 Quell games allowed you to "quit" the game. I have not been able to end the game I simply hit the home key and return to the carousel on my Kindle. Am I missing something? How do I quit the game? Since I downloaded this app, it has been draining my battery. If I am not able to quit the game, I will have to remove it from my device.