I just baked a 12 & 8 together in my oven. It's a brand new oven and is level inside and out, including th rack.

The outer side closes to the side of the oven did not rise to the top of the pan. I was trying to conserve time here, but now I have 2 cakes that are lop sided. the center and other side rose perfectly.

Can I bake the other 2 and hope they do the same and make it work? I really don't want to rebake and most of all waste so much cake? I have to decorate tomorrow for Saturday delivery.

Has anyone used both racks and it work? I've only ever baked on one rack place in the middle of the oven

I have baked on both racks. However, you may need to do some testing with an oven thermometer to see if the heat is even in the oven. Even if it's new, the thermostat could be off. Also, how much space was around the pans when they were near the sides of the oven? Enough room for air flow?

The other thing you could try is using a heating core or a flower nail or two in the pans. I've found that helps with leveling.

I got a new oven last November and I've had the same problem. I had one so lopsided b the time I trimmed it even, each layer was only an inch tall. Thankfully, it was just a cake for a small get together. Since then, when my cake is done, I put it back in the oven for an additional 3 - 5 minutes and it seems to be working. I haven't had any more lopsided cakes.

Is the oven fan assisted?

My cakes always bake lopsided. Haven't checked to see if it's because the oven isn't level or if the temperature isn't even throughout. But I did discover that if I give the pans a 180 turn half way through baking, they come out beautifully. I have baked four layers on one rack with complete success doing it this way. I also do it even if there's only one in there.

If it is a convection oven, it's because of the fan and you will have to turn your cakes halfway through. I currently rent a commercial kitchen and the 40 year old gas Blodgett has a high fan that cannot be turned down and I have to turn everything, including cupcakes, 1/2 through.
Also, oven have hot and cool spots. You just have to learn where those are in your oven and compensate. In this oven I rent, the right side is cooler than the left side and the back of the oven bakes more evenly than the front. I've cooked enough cakes in it that I know where those spots are.

Thanks everyone.

I did bake on 2 racks and they turned our perfectly.