I did a four-tier funfetti wedding cake in the spring. I tried just adding the rainbow colored jimmies to my regular white cake recipe as a test run, and it worked fine on a 9" round. That was WEEKS before the wedding. When I got ready to bake the layers, the 14" square totally sunk on me. It took me about three tries of adjustments to get it right...trying a different flour, changing egg amounts, reducing the amount of jimmies, etc. It eventually worked out, but it was very frustrating that something so seemingly easy to do became such a nightmare. My advice is to test your recipe first, then be sure you give yourself plenty of time to make adjustments in case it backfires. And I would err on the side of fewer jimmies in your batter. HTH!!