There's two ways of going about putting a road through hilly terrain and it depends on what is more important: the terrain or the road.

You've started with the hills, so really that's going to determine the shape of your road in many ways (both geographically and technically when drawing) so I'd say a simple solution here would be to cover a layer in a dirt/road texture, throw up a Layer Mask > Hidden on it, then use a soft brush to draw in the shape of road with an Overlay on the layer so the road contours follow the shape of your hills. Your other method would have been drawing the road first then building up the hills/terrain around it, but as you've already worked on the hills then might as well work with what you've got.

From here start building up main terrain features like trees, thick bushes, broken walls, large rocks, etc. generally the stuff that can be used in the map as cover, etc. Then build up the small details like smaller bushes and flowers, and finish with lighting effects at the end (at least that's how I go about it).