Well, I couldn't really come up with many options for this game...the only one I could think of was to keep track of the number of moves it takes to complete the game. This should be pretty straight forward for you at this point, so why don't you see if you can do it on your own? Getting this to work would certainly improve your grade!
A more advanced option would be to not only keep track of the number of moves, but to keep track of a number of "Low scores." If you do this, then you'll be able to try to beat the best players of the game!