Not to bad for a 'first attempt' - though you do have some "river violations"...
Rivers don't generally split as the approach the sea/coast/etc. If they do it is only for a short time or for a delta of some sort at the mouth. Try thinking of a river system as a tree with the 'branches' starting at higher elevations and merging to become the 'trunk'.
Keep at it and you'll be a "happy mapper" in not time