Is there a way to make the Pen list smaller and the chart bigger in an easy chart?
Are you referring to the Pen names referenced by 1 or the legend referenced by 2 as shown below?
In the case you are referencing the legend as denoted by 2, you can remove it completely through the properties.
Both of those options in the screenshot above can be hidden, so if you are looking for a smaller option, I would potentially say to hide the Pens, and move the legend to the left side. This will give you the effect you want, but you will lose the check boxes to show/hide/remove individual pens.
So I might recommend a small button or something to swap those properties so that you can still access those options.