You don't need to be an excel wiz. All you're doing for a simple sheet is entering an account name, then each fund and categorize it as US stock, US bond, International stock, as examples. I color code, so US stock is light blue.....international is red and bond is purple.
At the bottom, I do a function of sum of, all the us stock, then total all us bond, then all int stock.
Total all.
To right of each of the function sums, divide by the total. There's your percentage.