When you export a map, click the "Options" button to enter the dimensions (width/height) you like. If you save as a *.jpg have a look at the "quality" text box. Export the map a few times using different settings to get a feel what you are doing.
The overall shape is good. Try to reduce the amount of mountain symbols a bit. They look too crowded now. Also start with hills, then mountains and finally the giant snow covered peaks in the middle of a mountain range.
Have some rep for posting your first map!