To fix this issue, you need to change the Paper Size for your Dymo when you print.
As shown above, you'll need to set your paper size to "1744907 4 in x 6 in". There are lots of options to choose from in the Paper size drop down. Fortunately, though, the one you want is pretty easy to find. It's the second-to-last option, at the very bottom of the list:
