Should have instructed better. I thought that number keys are used to move too, so I didn't care until I got stuck and had to spam all the keyboard to find out. A seperate sentence like: "use number key to reserve the box and tile that have same number" or something like that would really help out the player.
Other than that, the game is quite fun and creative, so well done! I'm looking foward to new levels and mechanics, if you decide to continue developing it.