I like where you're going with this scene!
I think you simply need to add more elements to help increase the depth and add more interest at the same time. Like a few more animals, maybe some trees or a mountain range in the far background, possibly even something in the immediate foreground. You could also push the atmospheric perspective and make the grass far away blend with the sky color even more.
I did a quick paintover of what it could look like. Hopefully it will give you some ideas as I'm sure you can turn this into a beautiful piece