ArtRage print support is relatively basic and simply sends the printout to the printer software without sizing or scaling, at its native size and DPI as set up when the image was created ( There are not scaling settings in ArtRage itself so I imagine that you are using your printer software's scaling feature to attempt to scale the image ). It sounds like your image is not set up for the correct size and DPI in ArtRage. You could try resizing the image in ArtRage ( Edit, Rescale the Painting ), and make sure the size is what you want in inches, and that the DPI setting matches your printer's DPI. Then you can skip scaling the image with the printer software and print from ArtRage.
Also, you could try is to export the image as a lossless format like PNG, then print from another application which may give you the customisation you want.
If you're on Windows, an application such as Irfanview ( downloadable from http://www.irfanview.com/ ) will allow you to specifically scale the image to fit different sizes of paper and so on within the application itself, so you could download that and use it to open the image. The Windows preview application can also print exported images, but its range of different sizes isn't very varied.
In future though, what you can do, is to find out what DPI setting your printer uses, and when starting your painting in ArtRage ( File, New Painting ) choose the size you want and a matching DPI and it should print out at the size you are after.
Hope that helps!