Not sure what others said below as I'm too lazy to read it (:P), but just wanted to offer the advice of using the simple WorldBoundaryShape3D (in ColliderShape3D) would fix the going through the ground issue I ran into before I fully read the controls.
And (again, others may have said this) just the general advice of starting with a smaller set of elements to get working, and then layer on others if you have time. Not that I'm the best at this either, but game jams seem to ultimately be about time management and recognizing what you can realistically accomplish. Leaving the extra time for the polish at the end is essential for a more accessible experience.
That said, this is an ambitious game and I had fun playing what you got together!