I baked a 12 by 18 I leveled batter in the pan, it came out even but when I took it out of pan it looked like this 

Unfortunately you pic doesn't show much - at least I cannot make out what you consider wrong w/it.   From what I can see it looks like most baked cakes - maybe a bit short....did it rise as usual?  Are you sure you put enough batter in the pan?   Tell us what you think the problem is. 

All is good not, once I put a thick layer of buttercream were it was uneven,  it isn't as noticeable