You don't even have to generate terrain, just use ''Game of Thrones'' or ''Base of Ice'' or what ever those are called and copy paste their scene codes.
I used ''Game of Thrones'' for Skyrim, just for reference.
I am talking about the already existing (empty) scene called Game of Thrones.
Having said that, I do think you ought to change to a larger scene. You can then just redo the terrain as you did it, but then on a larger scene.
I would also do the rivers at the end btw, because if you do the rivers beforehand they will only restrict you. Mountains are more important than rivers aswell, because they actually make scenes feel larger.