If you have a larger seating chart or stadium style venue, you will need to adjust the settings to view the whole image.

This is an image of what it looks like in Preview.

When you look at the Design section, this is what you see initially. The Stage Settings defaults to 1200 x 1200.

Change 1200 x 1200 to 2400 x 1200 and click the blue Apply button.

This is what you'll see. You can adjust the Zoom below the Apply button if you want to see more of the chart.