The scale will only move the configuration of the image around mate. I say if there is a bit missing check the PS image...you may have cut a bit off accidently??

Ok you have to put an image on the inside as well?? or texture?? weird. How would they see it or are you leaving the top or side open to see inside?

If it wa me..I would fold the box...then extrude inward to get thickness. Then pick outside faces..apply red shade and hide it. Then apply another shade to the inside (yellow).

Then UV the 2 different shades and apply the checker shade to see if it is all relative (you done this before at all?)

Then snapshot the UV layout..take to PS and do your thing. Bring it back and apply the image to a shade and then assign to the model...presto.

Cheers bullet