I was working on this piece for a while
I see, thank you very much for the explanation! I found it hard defining things in my head and then later in the piece, that's why it's probably a bit difficult to make out...
Some pixel rows/columns in your preview are stretched or squashed and not in line with a perfect 200% scale. Most likely you used 190% or something else close to 200%. You can see this yourself if you zoom in and compare with the actual image.
Interesting piece though I wish some things would be defined a bit more, the only parts I can really make out are the building in the middle and the moon. Is the building on a mountain, or a pile of rubble, for instance? It's hard to tell.
What do you mean? I'm aware that it's not the best preview.. but how are they not uniform?
The quality of the preview does not really do the piece justice. Make sure that if you re-size pixel art, all the pixels are uniform.