Any way to make the line gradient tool stop before continuing to the edge of the picture?

So I have this picture of my friend and his girlfriend watching the sunset on the beach. I want to setup a line gradient for the sky, another for the water, and a thrid for the sand. But when I use the line gradient the highlighed area simply goes from where the gradient is to the end of the image. Is there a way to set up a gradient so it goes up to and stops at the start of the next one? Any help would be appriciated thanks!