Given that you have gone to the trouble of creating the image it would be an idea to replace the sky with something more fitting. There are lots of sites that have free backgrounds for such things.
The castle is out of perspective, I don't know what photo editor you use but have a look and see if there is a Perspective tool.
Crop out more of the foreground black.
The castle appears to have a lot of fine detail that cannot be seen, this can be brought out by sharpening the image.
I used photoshop on a copy from the screen but it will give you an idea. I didn't crop so maybe you won't need to. You have the original so you will be able to do much better......
