Cool concept! And it's satisfying and puzzly to play.
As others have mentioned, I like that there are lots of levels and they're well-designed.
The red rectangle seems like it needs a physics rework. It feels like maybe it's being simulated using a Rigidbody, but when it's moved by the mouse, the non-physics-based motion causes the simulation to behave unpredictably, especially when colliding with the player. Maybe using a kinematic Rigidbody or trigger would help?
The connection to the theme feels a little loose? I guess the various objects you can move around are technically resources, so it sort of works? I dunno.
It's hard to decide what to suggest for improvements, because the game has everything it needs to be an excellent prototype! I think my only suggestion to make a better jam entry would be to add music. Adding a third-party music asset is really nice and takes almost no time out of your budget, especially if you pick something out before you start.
The game is missing a lot of little bits of polish that I normally expect in game jams, but that I guess are fine not to have in a three-hour project. If you keep working on it, remember to emphasize key gameplay events like jumps, death, and victory with appropriate sounds and animations, and to add some sort of transition so the game doesn't instantly snap between levels.
This is a really well-designed game; well done!