The last digit is a check digit. Try to enter the first 12 digits to http://www.upcdatabase.com/checkdigit.asp and you'll see that the last one can be calculated from the first 12.
If this manual I googled, is correct for your device, you can change the settings of your bar code scanner by scanning appropriate barcodes from the manual. You probably want to change the "Transmit UPC-A/UPC-E/UPC-E1 Check Digit" settings, see page 160 on the PDF.
Try scanning the barcode labeled "Do not Transmit UPC-A Check Digit". That should configure your scanner to transmit only the first 12 digits when scanning UPC-A barcodes.