The correct turn to get the snake to enter the maze is
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×8, 18, or 28. As you have found 9, 19, or 29 does not work, if you are leading it through the maze as in the intended solution.
The problem is, the snake does not start out with the correct parity to enter the maze on that turn. No matter how many times you lead it around the room, that snake will never put its head in the maze when you want it to... unless you do something to change its parity.
To change the parity of the snake, you need to
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×stop it from moving for an odd number of turns.