The best thing to check is the size listed on the live view (main preview in Qimage). In Windows, you can do that by hovering your mouse cursor over the print on the live view to show the size. On the Mac (if you are using Qimage One), you can click/select the print on the page and the size is shown under the live view (on the status bar). The size you see is the exact size that is sent to the driver when you print, so if you see "11.0 x 14.0", you know Qimage is sending the correct size. If you get anything other than the listed size, the driver is modifying the size internally. This can happen for a number of reasons, the most common being borderless expansion or scaling (reduce/enlarge).
Some drivers such as Epson drivers can actually lead you into scaling without you realizing it. For example, in the Windows driver, if you select anything other than "Same as Paper Size" for the "Output Paper" selection, it will scale your prints. As an example, some people are tempted to set their paper size to 11x14 and also set the "Output Paper" to 11x14. This causes the driver to scale because unless you print borderless, there are non-printable margins on the page and it will try to scale an 11x14 print down to something like 10.266 x 13.766 inches (the allowed printable area). Instead, you should always choose "Same as Paper Size" so the driver doesn't do any scaling.