Haskell: parse error possibly incorrect indentation or mismatched brackets

When I try to use the function below to implement a function like below the compiler return

parse error (possibly incorrect indentation or mismatched brackets)

The function:

demo 8 [1,2,3] should return [1,2,3,1,2,3,1,2]

 demo :: Int -> [a] -> [a] 
    let n = 0 
    demo arg [] = [] 
    demo arg (x:xs) = 
         if arg <= length (x:xs) then
             take arg (x:xs) 
         else
             let (x:xs) = (x:xs) ++ (x:xs)!!n
             arg = arg - 1
             n = n + 1
             demo arg (x:xs)

How can I correct that? Regards!