Unfortunately there is no way set the final barcode width ZPL. It does adjust to the amount of data you have. The width is a scale of the individual line or dot widths. The only way to do this is to use outside tools to convert the barcode into an image. Several of our design partners have this software that will scale to specific width requirements. The other way is to have your code change the width based on the amount of data dynamically, but that doesn't fit the XML framework you are using.