Hi Sandy,
I had a look at your listings’s source code in Editor mode.
As I already mentioned the HTML there is all mixed-up. It somehow uses code from the old GarageSale 5 (!).
To be honest, it would be a better idea to re-make* the whole item description. At least for your most important listing.
However, as a very quick and dirty fix you could add the following code into the footer field in the GarageSale preferences > General and restart GarageSale afterwards.
<style>#gs-descSpecialDiv p,#gs-descSpecialDiv font,#gs-descSpecialDiv .Apple-style-span {line-height: 1 !important}
#gs-descSpecialDiv h1 {font-size: 25px;}</style>
*How to re-make the item description without loosing the text:
Copy the whole text from the item description in Preview mode, switch to Editor mode, clear the item description field there and paste in the copied text. If you then switch back to Preview mode you can edit the text and select a design as usual.
Regards, Kristian