The most likely reason is that your label is not properly formatted for 4 x 6 label printing. ITPP941 prints exactly what you see on your screen in the same orientation. So if the label looks side-ways on your screen or if it has a lot of white space around the label, ITPP941 will print it side-ways and with the same amount of white space.
If your label is 4 x 6 but just provided sideways, you can setup ITPP941 to rotate it for you automatically:
During the print prompt, select your label size under Presets, then navigate to Printer Features -> Page Options and Select 90 under "Rotate."
Go to Control Panel -> Devices and Printers -> Right click on ‘Label Printer’ -> Printer preferences -> Go to Page Setup -> Under Orientation choose Landscape and Click Apply / Ok.