You need an application capable of ignoring the margin (Standard is 4mm)
Acrobat/Reader will do so, try saving the file to pdf
Then you can see the standard reduction (Scale 96% and the gray bit around the edges)
Set scaling to none and the image will not be reduced and go to borderless
But keep in mind, this is a toner based output device, you are not going to get a borderless print, that isn't possible, you are still going to have a border around the page, it will just delete any of the image that was going to be in that space.
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