Julie - from Ottawa, OH
The hump that you are referring to is called a cake "crown", or sometimes "dome." You're not doing anything wrong - a cake crowns because the sides of the cake that are touching the hot pan cook faster than the center of the cake. You can greatly reduce, and often completely eliminate that hump by using Bake Even Strips. These strips slow down the baking on the sides of the cake so that they rise more evenly along with the center. They are easy to use, and I highly recommend them.