I am not a Baker and I will not pretend to be but here are some tips to help with baking a flat top cake.
The top makes a rounded bump simply because the side closest to the edges of the pan heat faster than the middle of the pan.
How to Bake a Flat Top Cake
Here are some suggested ways.
1. Use aluminum foil and place on top of pan cover it.
2. Simply cutting the hump off with floss or thread or knife.
3. Cover pans with medal caps.
4. Use cooling strips to help the sides to bake more evenly.
5. After filling the pan with mix simply tap it on the counter a couple times releasing any air bubbles.
Topic: How to Bake a Flat Top Cake