Use the arrow keys to get to the X It gets harder as you complete more mazes and once the TILE SIZE variable is less than 12, it kinda gets broken. If you want the hardest level, go into the game. Go into the Maze sprite, and find the "When Flag Clicked" and right under it, it says "Set TILE SIZE to 42". Changed that to 12 or even 11. Feel free to hide the Time variable if it is in your way.
Thanks to @griffpatch for the YouTube tutorial