The issue isn't the thirteen room tiles, it's the four gem depot tiles (which makes a total of seventeen, plus the start and exit tiles).
QFT. Queen Games could have done a better job of showing which tiles are used in every game. The start and exit are obviously needed, but no one should forget to keep the triple-gem-altar rooms.
On a tangent, a while ago I saw a group playing the game. I was playing a different game at the next table, but I kept looking to see how they were doing. I noticed that they had a lot of tiles on the table. Sure enough, they were using every tile included in the box! The game seemed much easier to them after I let them know their mistake.