eishiya is correct.
use the pencil icon under the art to upload the art in the right panels and hit submit again.
Looks like you got the images backwards. The bigger piece should be the "detail" file (it's weird terminology). You don't need a detail file at all for this one though, since the whole thing fits as the preview file.
haha I was also confused when i saw the upload. But was thinking maybe I just forgot how it worked. Thanks for the heads up!