if you are using paint.net, try using multiple layers for things like this:
layer 1 = sky
layer 2 = clouds and sun(or separate layers for those if you want)
layer 3 = mountain
the sun is the only thing that looks bad, but the other things are decent.
better clouds than i can make anyway
oh and also try to make a separate image that is scaled up a few times using nearest neighbor mode, so people can see it better
