I have 9" cake pans my recipe calls for 8" how do I adjust the recipe to fit?

You can bake in bigger size of pan then desired shape. Take couple of thick baking or grease proof paper. Keep it on Aluminum pan and make the required paper box. Place in the pan you have, close to one wall fill the space with baked beans or any beans pour your batter. Bake you will get the size of cake your recipe mentions