The label size setting may be wrong.
Check the label size setting as follows:

1. Connect your computer and the printer, and then make sure that the printer is turned on.
2. Start the BPM (Brother Printer Management Tool), and then click the Printer Configuration button.
3. Check the Paper Width/Paper Height settings in the FBPL tab.

The Print Head tension may be wrong.
Check the Print Head tension settings as follows:

1. Adjust the Print Head tension using the Print Head Tension Adjustment Knob.
2. Choose one of six levels of tension adjustment depending on the media width you use (1″ - 2″ (25.4 mm - 50.8 mm) or 3″ - 4″ (76.2 mm - 101.6 mm)).
   
   The recommended Print Head tension values are:
   1.  For 1″ - 2″ (25.4 mm - 50.8 mm) media width
   2.  For 3″ - 4″ (76.2 mm - 101.6 mm) media width