There's a slight outline where you've cut the feet from the background. The rainbow background you've added also looks very flat, with no shading or depth to match the feet so obviously pasted on top. Perhaps a very slight bit of shadow to correspond with the feet will help.

The thought was to have the background as a color chart from a distance, on a wall to see what color you want the nails done in. With a choice one can see better than looking at the small dot on the lid.

GL

Interesting explanation, author. I'm glad to have it, since my initial answer to your description ("The image tells it all" was "Ummm... no, it doesn't." Maybe it's because I do my own nails. Good luck. MossyB makes a good point about the masking. Expanding your selection by 1 or 2 more pixels would remedy that next time.

**CORRECTION: CONTRACTING your selection (make the selection smaller than the outside edge of the object you want to keep) by 1 or 2 pixels. Sorry! Another way to smooth the edge is to feather it by 0.5 pixels before the chop.

Thank you for all the input. Everyone
I try to use all the helpful information that I can.
Being new to PhotoshoP and finding it a fun way to express ones views and imagination by simply looking at something, than trying to apply that to the project, makes for a fun way to learn through trial and error to refine the art.