:-(
I feel stupid, I don't understand what I should do.
You won't get the cat from 10,17 to 10,16, you need to come in from another direction. Take a look at the surrounding rooms and see which ones have two-space-wide exits. (remember to look at the room you will have to come from, since exit and entrance sizes might not match.
On a related question (although how it's related might not be immediately evident) have you learned yet that a dead cat can read signs?