Adding a Horizontal Line for "Goal"

[reneev]

I currently have a chart with vertical data. I have figured out how to add a horizontal line by creating a new series which shows the "goal" however, the line doesn't span across all of the vertical lines. It starts in the middle of the first vertical data point and ends in the middle of the last vertical data point. I want it to go all the way through to the ends. How can I do that?

I'd show you a screenshot but I can't figure out how to add an image here.