3x3 Tunnel Computer Craft Script

print("Conor's mining program!!")
print("Please place turtle at bottom left of 3x3")
write("Please enter the length of the 3x3 tunnel: ")
local number = tonumber(read())

local function mineForward()
    while turtle.detect() do
        turtle.dig()
        sleep(0.5)
    end
end

local function checkFuel()
    if turtle.getFuelLevel() < 200 then
        for i = 1, 16 do
            turtle.select(i)
            if turtle.refuel(0) then
                turtle.refuel(1)
            end
        end
    end
end

local function returnHome(number)
    for i = 1, number do
        checkFuel()
        turtle.back()
    end
end

local function threeByThree(number)
    for i = 1, number do
        checkFuel()

        -- go to bottom left corner and position
        mineForward()
        turtle.forward()
        turtle.turnRight()

        -- remove left column of 3x3
        turtle.digUp()
        turtle.up()
        turtle.digUp()
        turtle.up()

        -- go to top middle of 3x3
        mineForward()
        turtle.forward()
        mineForward()

        -- remove the 2nd and 3rd columns
        turtle.digDown()
        turtle.down()
        mineForward()
        turtle.digDown()
        turtle.down()
        mineForward()

        -- go back to bottom left of 3x3
        turtle.back()
        turtle.turnLeft()
    end

    returnHome(number)
end

threeByThree(number)