Digging turtle. level an area

args = {...}
length = tonumber(args[1])
width = tonumber(args[2])
needFuel = true
if not width or not length or #args ~= 2 then
    print("Usage: "  .. fs.getName(shell.getRunningProgram()) .. " <length> <width>")
    print("<length> is the amount of times it will go forward from the starting point")
    print("<width> is the amount of times it will go to the right of the starting point")
    return
end

while needFuel do
    if turtle.getFuelLevel() < 300 then
        print("I need fuel!\nWhich slot must I use?")
        nSlot = tonumber(read())
        turtle.select(nSlot)
        if turtle.refuel() then
            print("Fueled! I now have " .. turtle.getFuelLevel .. " fuel.")
        else
            print("No fuel in that slot.")
        end
    else
        needFuel = false
    end
end

for i = 1, length do
    for k = 1, width do
        while turtle.detect() do
            turtle.dig()
            sleep(0.4)
        end
        turtle.forward()
        x = 0
        while turtle.detectUp() do
            turtle.digUp()
            turtle.up()
            x = x + 1
        end
        for l = 1, x do
            turtle.down()
        end
    end
    for k = 1, width do
        turtle.back()
    end
    if i ~= length then
        turtle.turnRight()
        turtle.forward()
        turtle.turnLeft()
    end
end

-- Return to start
turtle.turnLeft()
for i = 1, length do
    turtle.forward()
end
turtle.turnRight()