Text within a gameObject boundries.

I am working in a little project and I want to show text within a rectangle. for that I use a sprite(rectangle) and a child that contains a TextMesh as component.

The text change during runtime, and what I want is to make the text always centered and within defined bounderies.

All I can think about is to set the fontSize/Character Size depending on the text length.

But then I wonder is there a better way or a build in functionality.

Thanks before hand.