How can i make this snake use the slide method

I have been writing this fior a little while. well on and off for a couple days, If I try to use the snakes slide method the snke kinda goes off to one side of where I want it to go. and if you look at my code I need it to go to specific spots for it to function correctly if anyone has ant ideas Id be glad to hear them. I would just know how to mae it slide so it looks right thanks