Capability of Generative Fill?

This is probably a stupid question, but I've been trying to experiment with the new Generative Fill feature (some of you might recognize that I created a separate thread last week about how to actually access it). Forgetting about the fact that I can't even figure out how to access it for just a moment, I'm simply trying to figure out just what it is capable of. The screenshot I've attached to this post features an image I'm working on that I like overall but got a bit sloppy with, I think, in terms of the edges, as the left side of the lake is cut off. There's no way to use Generative Fill in a way that essentially provides a realistic-looking end to the lake, is there?