If your image is wider than the media, you sometimes need to rotate it and it will be the right size unless you need to tile the job. Not sure if 10 does it, but in 11 there is the rotate option when importing files. Or you can open it in job editor and rotate it there.
I think this happens for certain types of files. I know it doesn't always happen for us but occasionally. It was never much of issue for us cuz it's a quick fix.