Working on my first map and I have a bunch of questions

[bill]

I created my first map using Giide's Ascension's Atlas Tutorial in GIMP.

WIP2 MapFINAL_copyv3.png

On the one hand, I never thought I would be able to make a map of this quality with a free program in just a few hours. On the other hand, I came away with more questions than when I started:

1. Where did I go wrong with the mountains? I know there was a step where I could edit them down, but I assume that I made a mistake before that point in order to have so many gigantic plateaus. I tried it twice and got similar results both times. On the flip side, I'm definitely going to incorporate a gigantic, impassible plateau into my next fantasy world.

2. How do I make hills? All of the lighter green spots are hills, at least according to the Hills layer I created in the tutorial. They look more like plains to me on here.

3. Why are the colors so different on the exported .png? I attached a screenshot showing a sample of the coloring that I see in GIMP. Am I doing something wrong here? It may be less noticeable, but I think one of the biggest problems is the black splotches that appear in the exported version but just add a hint of texture when viewed in GIMP.

I would also love any other feedback or suggestions.

Thanks for the help!