Cool! I've always loved Kirby's Dream Course!
Btw, I have a suggestion: in the future, you could make it so that the user of your tool could test their new stages by simulating shots. For instance, they would place Kirby somewhere in the level they are designing and adjust the shot parameters (the same ones as the ones you use to make Kirby move in the game) to see whether it's possible or not to beat the level. There could even be a feature to test whether it's possible to make a hole in one in the level.
I don't know how hard would it be to implement this. I imagine it wouldn't be extremely hard if you know the physics of the game.
Anyways, nice job with this! =)