[julvito]

[davidmattingly]

You have a terrible fringing problem going on throughout this piece. When you cut a mountain or any other element out of another photograph, you must make sure that the light pixels on the edge don't transfer over to your new composition. If you go to the top menu and choose Layer>Matting>Defringe, you can choose a number of pixels to take off the edges. If the fringe is white, you can use "Remove White Matte", or black matte if it is black. You can also just break down and paint the edge so that it removes the fringe.
Also, remember that anything in the foreground should have more contrast than objects in the background. In your piece, your foreground mountain has less contrast than the mountain directly behind it. Remember the 3 types of perspective: atmospheric, linear, and color. The linear perspective on your ruins looks pretty wonky here--it would be of value to set up a set of vanishing points and figure out where the walls would vanish to.. I see that the building here were not set up on a grid, but what you have here looks like the perspective was taken out of another photo a plopped in here.
Hope that helps! Good luck on the midterm