Hey Stephen!
If you make the background a child of the text (I'm assuming the top line), you can have it match the width length of text using the auto scale feature. I have a similar setup for some of my graphics and have attached a picture below.
Take note of object manager structure and auto scaling in the bottom right corner.

If you don't have that option due to being on an older version of Xpression (or any other reason), you can adjust it in Visual Logic like our friend, Azathoth Son of Cthulhu, suggested. I have also included a picture of what that might look like.
Take the bounding box width of the text, add the difference in pixels you want, and set it to the width of the background.

Let us know if this helped!
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John Spitznagel
Video Production Engineer
Elon University
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