View difference between Paste ID: XhzKKeTD and xw45DNzy

 local length = 61
 local width = 61
 
 local function refuel()
 	if turtle.getFuelLevel() < 50 then
 		local prev = turtle.getSelectedSlot()
 		turtle.select(1)
 		if not turtle.refuel(4) then
 			print('Need more fuel')
 			while not turtle.refuel(4) do
 				sleep(3)
 			end
 		end
 		turtle.select(prev)
 	end
 end
 
 local function tryForwards()
 	refuel()
 	while not turtle.forward() do
 		if turtle.detect() then
 			turtle.dig()
 			sleep(.5)
 			while turtle.detect() do
 				turtle.dig()
 				sleep(.5)
 			end
 		elseif turtle.attack() then
 		else
 			sleep(1)
 		end
 	end
 end
 
 local function advance()
 	if turtle.getSelectedSlot() == 16 then
 		print('Need more materials')
 		local empty = true
 		while empty do
 			for n=2, 16 do
                 print (n)
                 if turtle.getItemCount(n) > 0 then
                     empty = false
                     turtle.select(n)
                     return
                 end
             end
 			sleep(3)
 		end
 	else
 		turtle.select(turtle.getSelectedSlot() + 1)
 	end
 end
 
 local function placeBlock()
 	if not turtle.detectDown() then
 		if not turtle.placeDown() or turtle.getItemCount() == 0 or turtle.getItemDetail().name ~= "minecraft:stone_slab" then
 			while turtle.getItemCount() == 0 or turtle.getItemDetail().name ~= "minecraft:stone_slab" do
 				advance()
 			end
 		end
 	end
 end
 local function turnAround(i)
 	turtle.placeDown()
 	if i%2 == 1 then
 		turtle.turnRight()
 		tryForwards()
 		turtle.turnRight()
 	else
 		turtle.turnLeft()
 		turtle.forward()
 		turtle.turnLeft()
 	end
 end
 turtle.select(2)
-for i = 1, length, 1 do
+for i = 1, length-1, 1 do
 	for j = 1, width-1, 1 do
 		refuel()
 		placeBlock()
 		placeBlock()
 		tryForwards()
 	end
 	turnAround(i)
 end