Because the shopping cart is metal, it reflects much of the blue background. The Color Range method selected some of this reflected blue because it was too similar to the surrounding mat color. There's no need for perfection, but some of the more obvious pieces should be removed from the selection. Make sure the subtract from selection method is chosen, and pick a masking tool. I find the Polygonal (or "Point-to-point") tool to be the easiest to work with when creating selections manually.