Upon further review I found the Margins are available when you select Text Caption, but not when you place text inside of a Smart Shape. Since I need the text box to point left and right instead of up and down, I created Smart Shapes. BTW, I am using Captivate version 6.0.1.240.
I realize I could create my own Text Captions, but I don't want to any more time than I have to to develop this project.