Epson ET 2820 - 4 x 6 points

[ColinG]

When printing without borders to 4 x 6 inch paper I end up with a white band about half inch thick on the right hand side of the image, in other words the print does not fill the paper. I am on Mac and this happens no matter whether I am printing from DxO PhotoLab or Lightroom. If I print a 10 x 8 the result is as expected. Any ideas how to cure this?

Thank you.