Thanks for asking, I would love to elaborate because I honestly think this game has potential. well, for starters, you would want it to test the player's mastery of the gravity mechanic - the games signature mechanic.
So You want to make something harder but not necessarily longer. For instance maybe you could make a more complicated version of the "navigate-a-box-through-a-maze-while-on-a-moving-platform" section. or maybe you could make the player catch a box from out the air with a well timed beam. or combine the two, something the player can feel good about when they finally get right.
You know, something that makes the game more challenging by using the key mechanic in an interesting way rather than just make the player jump more times over longer distances while carrying a box.