Modification: Human To Mermaid

If I may, this still needs a lot of work. You can easily avoid your pieces looking like a beginners work if you take more care about the edges, e.g. on the hair and on the edge of the tail. I also would have rotated the girl a bit to make her position fit to the rock.
Another thing, I'm not sure where you got the original picture, but be aware that google and stuff are no legal source for manipulation ressources. Join DeviantArt if you need free stock.
Well, after a crapload of criticism: Keep it up, quality comes with experience. All the best to you.