Print image scan larger than actual size

[Ofnuts]

Scan it it higher DPI than your target printer (for instance 600DPI if you target printer is 300DPI)

In Gimp (or in another capable image editor) just change the print definition to 300DPI to double the physical print size (thisis in Image ➤ Print size in Gimp.

See this for the explanation of the magic.

This said, a much simpler approach:

• Start a document in your usual word processor (MS Office, Libre Office)
  
• Import your image  int the page
  
• Resize your image by dragging the image edges
  
• Print the page