I'd recommend you start over. I always start patterns that are mirrored in the x axis by figuring out how to do a quarter of the pattern.
I also use a view, so that if you want to change the icons you can.

And so I start with:

    def palindrome(n):
        view = list(map(str, range(n + 1)))
        for size in reversed(range(n + 1)):
            half = view[size:]
            print(''.join(half))

    palindrome(3)

<!---->

    3
    23
    123
    0123

After this we know to use `view[size]` as the center, and we repeat it `size` amount of times.

    def palindrome(n):
        view = list(map(str, range(n + 1)))
        for size in reversed(range(n + 1)):
            half = [view[size]] * size + view[size:]
            print(''.join(half))

    palindrome(3)

<!---->

    3333
    2223
    1123
    0123

From this you will then just have to mirror the output:

    def palindrome(n):
        view = list(map(str, range(n + 1)))
        for sizes in (reversed(range(n + 1)), range(1, n + 1)):
            for size in sizes:
                half = [view[size]] * size + view[size:]
                print(''.join(half[:0:-1] + half))

---

Going forward, you could enter `view` into it and make it output whatever you want.

    def palindrome(view):
        n = len(view)
        for sizes in (reversed(range(n)), range(1, n)):
            for size in sizes:
                half = view[size] * size + view[size:]
                print(half[:0:-1])

    palindrome('.|.|')

<!---->

    |||||||
    |.....|
    |.|||.|
    |.|.|.|
    |.|||.|
    |.....|
    |||||||