KateG, I think the issue was that when I thought I was sharing the graphic, it over-laid the GoToMeeting screen so there was no way to see what participants would see. And last Monday when it happened, nobody there to confirm for me!
I'm accustomed to seeing a black background with squares for whatever I'm sharing in one, plus one for each participant. Today I took some time to fiddle around with it and change the sizes of the respective screens, and I believe it's probably there. I have the little message saying "you're sharing your screen" so I'll trust it. Thanks.