Looks like you are getting the idea
, gimp just takes time/practice. I cut and paste a lot then use the smudge tool to blend all the little polygons edges. Still havent got the hang of iwarp yet though.
FYI, for the square corner, I just drew a white line (holding the shift key and clicking when the next line segment looked in the right place) where I thought the crease should go then smudged it a bit (the finger looking thing).