Large format chart printing

I have been trying to produce a large (20x15") ancestor chart. I am using the Charts (large format) selection. I select “custom” and put in the dimensions. It’s saved as a PDF but when I open in Adobe acrobat it’s only 8.5x14. Can’t seem to find the solution. Thanks

When I create custom 15"x20" portrait ancestor chart, save, then open in my Edge browser… the Document properties (under the gear icon) shows 14.67" x 22.67"