ah HA! I see what I did. So, for the box nearest the stairs, I just interacted with it from the SIDE, and, thinking it was a sprite trigger, I did not interact with the box again from the front by standing in front of it (I assume it was an item trigger).
Also, the aspect ratio of your game on itch is a bit squashed (no pun intended), so usually for Bitsy games you would fix the viewport to 560x560 or something (though you did have a fullscreen button which I used).