If it's the second frame of the three-panel strip, then, as another commenter hints, the trick is not to double back. You must complete a circuit around the map. I got frustrated and quit long before trying this until reading that comment, but it (arguably) pays off.
It's the first frame, I read the comments and still I don't understand. The game is too stressful for me, I give up haha
or before I get the key, or as I get the key...
I don't play video games at all so playing a game where I have to figure out the goal. Ugh.