At this scale the river would be way too fat for a realistic-type map. It has a great shape, though, and would like very fine on a regional or city scale map. A map of this scale (more in line with a nation scale rather than regional) would have a lot more variation in the geography...more hills, more rivers, more towns, etc. The small size of the image itself makes too much detail a problem. If you choose not to represent those things then it will look a bit odd so I would suggest a different style - something more along the lines of a line-art or hand-drawn map might be better and simpler. If you want to pursue the more realistic style then you're going to need more rivers as a minimum. My guess is that this is done in Gimp so look through the Tutorial subforum for tuts that have the word GIMP in the title. Forgoing that, just give us a name of or link to a map that you like and we'll help ya from there.