The Dymo 450 is not recommended with Pirate Ship. We hope to add more label sizes in the future, but until then, the Dymo 450 print is smaller than standard 4x6" shipping labels.
However, we have had users successfully print "4x6 labels" with Dymo 450 label printers.
Here is list of label printers we recommend.
And here is a video of a Pirate Ship user explaining how he got his Dymo 450 label printer to generate successfully used labels:
Our PDFs are formatted perfectly for 4x6 labels, so again, a label printer designed for 4x6" labels is recommended.
These settings are not connected to Pirate Ship and so you'll want to reference your manual or call DYMO customer support directly if you cannot locate the problem: http://www.dymo.com/en-US/online-support-contact-us