Thanks for checking out the game, I'm glad you're enjoying it so far!
Some of the puzzles in the Cocoon aren't as clear as the others. It sounds like you are talking about the puzzle in the southeast corner of 1F. That puzzle can only be solved if you are physically in the Spirit World where you mentioned you can pick up the rock. I bet if you take another look you might be able to figure out how to roll the ball while you are in the Spirit World, but feel free to DM me if you'd like a stronger hint.
I hope you enjoy the rest of the demo!