The first one is a bit chaotic, but since it is pretty large, it could be a fun background though

For the second one; Although the stock (background) might not be the best to work with (with this render), try to blend it in a little bit; Use a soft (small) brush to erase the edges of the render.
Another thing you could do is add one or more gradient maps, this could help you, by blending all layers (more) together.
Anyway.. Keep practicing
