I would start by adding some perspective to the grass, thats the main reason it looks flat, in my eyes.
I duplicated your grass layer 4x and then merged them into one. You created the grass with a bit of an angle to it, so I used that to my advantage and placed 2x facing one way and 2 the other, so they helped create a vanishing point.
After I merged the layers, I transformed them, using Perspective (⌘+T and then right-click to select Perspective).
And then create your perspective, by dragging the top points together
I thought the grass was a bit dark, so I added a gradient to the top of it
And then I added another gradient to darken the bottom of it
I almost forgot to include these steps I took earlier, I added two adjustment layers to your grass layer. One for levels and another to bring up the saturation a bit (increasing the brightness like I did in the levels has a tendency to desaturate images)
It's not perfect and I could definitely invest a lot more time working on the grass, but if you play around with some of these things it might help, especially the perspective