Having major superimpose problems!!

[Ofnuts]

Possibly because when you used color-to-alpha everything became partly transparent. Color-to-alpha is usually not the right way to extract things from photos. If you extract was on a solid background you can extract it again like this:

• Use the wand selector to select the background
  
• Select ➤ Grow by two pixels so that the selection covers the edge pixels
  
• Use Color-to-alpha. It will only apply to the selection and the core of the subject, being un-selected, will remain fully opaque.