Whilst this might be officially be a demo disc, the full game can be unlocked on this disc!

On the Title Screen, press the following: Right, Left, Right, Left, Down, Up, Down, Up, Right, Right, Right, Right. 

A level number will pop up at the top of the screen, which you can change with your controller and you can then play the full game.

Overall, the disc is in good condition. There's some surface marks, but nothing which affects the gameplay.