Even the pros get a "hump" in the middle. It's my understanding that it's actually a good sign. If you want a flat cake, just slice that hump off.
Here's a cute cake recipe I found:
Preheat oven, get out utensils and ingredients.
Remove blocks and toy autos from table.
Grease pan, crack nuts.
Measure two cups flour;
Remove baby's hands from flour, wash flour off baby.
Remeasure flour.
Put flour, baking powder, salt in sifter.
Get dustpan and brush up pieces of bowl baby knocked on floor.
Get another bowl.
Answer doorbell.
Return to kitchen.
Remove baby's hands from bowl.
Wash baby.
Answer phone.
Return.
Remove 1/4 inch salt from greased pan.
Look for baby.
Grease another pan.
Answer telephone.
Return to kitchen and find baby.
Remove baby's hands from bowl.
Take up greased pan, find layer of nutshells in it.
Head for baby, who has fled, knocking bowl off table.
Wash kitchen floor, table, wall, dishes.
Call baker.
Lie down.