Use the Positioning tool to resize labels.

Labels normally autosize, meaning the text rectangle automatically resizes to accommodate the text you enter. Label text remains on one line unless you enter a carriage return or resize the label box.

Right-click the label and select Size to Text from the shortcut menu to toggle autosizing. When you resize a label, LabVIEW automatically turns autosizing off. You also can use the Size to Text? property to programmatically set whether the size of the text object changes according to the text included.
Note You can resize a string constant the same way you resize a label.
Note If you enable a vertical scrollbar on a free label on the front panel or block diagram, LabVIEW automatically disables Autosizing » Size to Fit for that label.