The title bar at the top of a box will not expand, so it is important not to make your box titles too long. This is rarely a problem in the wider center column, but must be watched for in the narrower left column.
If it looks like your title is not fitting, click on the Preview link at the top right of the page. Sometimes, the pencil icon in edit mode keeps the title from fitting, but it may be okay when actually published. The preview will show you how it will ultimately appear. (Of course if it still doesn't fit, you'll need to shorten it.)