Hey this is a great first jam game! My one recommendation is that you should lead your first level with something that shows off your main mechanic - for me I didn't get it until I got to the level with the timed platforms, and then I was like oh - I need to plan out how each loop is going to leave me with platforms and level elements in order to proceed. And that's a cool idea!
My other recommendation is to use a non-dynamic physics based collision/rigidbody for the boxes. With realistic physics and full rotation on the z-axis they can be a little difficult to precisely move in a 2D platformer setting.
Keep up the good work!