So I've done quite a few of these and at first, I figured it had been a year I was missing a step and looked up the instructions. No steps missing. Now when you do the four teleporter tiles and place the stairs, the very first step will delete the first two teleport tiles. If you delete the second two teleport tiles, the 2nd tiles of the stairs will disappear, leaving a hole to fall through. You can delete everything but the very first set of steps as seen in the pictures. ACK! See below.