Hmm, thats really odd, I've never encountered that problem... 1) How large is your resolution? I always work with 1000+ pixels in both length and width, so that way its quite big and you can reduce the filesize later. 2) Are you exporting is as a ".jpg"? Some other formats don't work so well.
The picture has a really warm and calming tone about it. And I like that about both the movie and your rendition of it, as in Tangled, Rapunzel didn't see the tower as a prison but rather as her home. =]