Thank you! :D
There's a power-up in the shop called the Thrilling Ladder. It's a little buggy and not well balanced since it went in last minute, but it lets you build upward so you can return to areas you've missed. The level design tries to encourage some "oo I see something interesting above me, maybe I should buy a ladder for tomorrow", but with the limited time we didn't really do a great job communicating that to the player.