If your barcode is not printing clearly, the source file wasn't created in the ideal quality. 


Please try this sample label here which was generated at the correct quality to test: Sample Label


Please try reducing your print speed (try 3mm/second) and your print density (try 3 as well) to see if you obtain a better result. 


On PC: 

Go to Control Panel > Devices and Printers > Right click on Rollo > Printer Preferences > Settings Tab 


Adjust Speed and Density 


On Mac:

Access these settings directly from the print menu as shown below.