Okay I've made two sheet cakes so far and each time the corners of my cakes are hard. And I can't seem to stop my cake from bubbling in the center. 
This causes the sides of my cake to be smaller and thin and the center really thick. I even out the batter the second time and that just made the center thin. What am I doing wrong. Does anybody have any ideas or can lend me a hand in making this cake great. I know someone has had to deal with this before. Help me
It sounds like you need to bake at 325 and put a flower nail or two in the middle to act as heating cores.
Thank you, I will try that. I'm glad someone replied to me. Thank you 
Have you checked your oven to be sure it is baking correctly? Sounds like something I had once and it was my oven. Seems that the elements were not heating evenly or something like that so the cake got high in the center cause it was cooking faster than the edges???!!!
New oven and it bakes like a dream, same recipe, same pans, same everything. I do agree that you may try lowering the temp. I almost always bake a few degrees lower that the recipe, and on my oven it has a "cake" setting.
Linda2530
I grease-only-no-flour my pans. The grease-only allows the batter to slide-up the sides of the pan more easily. When the pans are floured, the batter actually grabs-onto the sides of the pan, restricting the ability to rise to it's best height.
Also I suggest baking strips. here's the thread where I explain the science behind these and how/why they work: http://forum.cakecentral.com/modules.php?name=Forums&file=viewtopic&p=3467363#3467363
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