Just found this after watching your yt video, I think the current state of the game is quite impressive from a technical standpoint. From all the games in the jam, just moving around feels the most "smooth", the sounds are fitting and it does not give off the somewhat janky feeling of many other 3D entries at all.

As for the game, bummer that you could not finish it properly. Game design is hard, but you already had some interesting ideas with the bed, the speaker and scaling things midair, that surely could be incorporated into a full game (well, a full gamejam game anyways). As general advice, just sit down with a pen and paper, stop thinking about the technical side of things, write down all elements you have so far and think of combinations that could work as individual obstacles, than chain a couple together as a level, ideally ordered by difficulty. This jam was the first time for me as well where I made a game with a decently long level, and this approach worked quite well for me.

Heres some more ideas that could work in your game:
-Boxes that do not scale in all dimensions, but only one or two. Or give the play the ability to scale dimensions separately at will
-Make mass a separate dimensions to scale, independent of size
-Allow scaling boxes so quickly that is launches the player and other objects into the air or to the side
-Surfaces that reflect the scaling beam
-Ability to shoot yourself with a reflected beam and scale yourself
-Glass that only allows upscaling or downscaling beams to pass through

The difficult part of course is combining all these elements into increasingly hard challenges. I don't think there's a good way to learn that except just doing it and getting better.

Small side not, the Linux build is a bit borked for me, when I click the executable it launches like 30 individual instances of the game (which freezes my pc for a solid minute), then I can close all but one again and start playing.