I am in awe of the colors of this piece. They are so vibrant and eye-catching.
In regards to the technical work of this manipulation, you did quite well. I downloaded the image for the full view to look at all the little pieces of it. For the most part, everything is blended nicely. You did especially well with the model; the umbrella looks like it was a pain to cut out. But you persevered. The castle was nicely done as well, but some areas were missed. If you take a very small eraser and go around the edges, it would look perfect. There are also some random blurred areas throughout the artwork. If you took the sharpen tool to them, they wouldn't stand out quite as much (but only use it lightly; otherwise, the areas will end up pixellated).
The only thing I can really critique is the lighting/brightness of the piece. The model is especially bright, and she reduces the depth of the manipulation as a result. Her left side should be darkened and the right brightened (given the positioning of the sunlight). She also doesn't really seem to match the color scheme; there is no yellow or orange cast on her. The castle is also a bit too bright given its distance lighter part of the sky. These things are easily remedied, however, with quick level and color adjustments, as well as minimal burn/dodge tool use.
I hope this critique helps in at least the smallest way. If you have any questions, please feel free to ask.
Overall, this is a very stunning piece. Please keep creating.