So, you have to set a direction in every purple area, even if there's only one possible way. In this case, to go to the central square, you should follow the next sequence: forward, forward, right, right, left, and destination.
Even so, I've changed the map, hoping it to be easier to understand.
Thanks for your comment. Before publishing the game, I tested it with some friends, and I noticed this problem, so I tried to solve it in a nonwritten way (which I see didn't work). Because of this, I've uploaded a new game version with a written tutorial (which I hope works).
