Shape widgets can also be sized to the text they contain. Double-click a handle on a widget’s left or right side to automatically size the widget’s width. Double-click a handle at the top or bottom of a widget to set the height of the widget to its contents. Double-clicking a corner will automatically set both the width and the height.
You can also look in the Style Tab of the Inspector panel on the right. There are two little buttons for Fit Text Width and Fit Text Height:
Do note that if you change the text dynamically, the widget will not resize to fit the new text–it only works at page load. A while back I worked out several methods to try to work around this limitation in this thread:
…and another example applied to a basic text widget without all the repeater stuff:
