Hey John - That's a great question....and I don't know why you'd only see the one URL. Try replacing
arcgis-survey123://?itemID={you're storymap ID}
with
https://survey123.arcgis.com/share/{you're storymap ID}
The itemID and URL after share are the same. For example
https://survey123.arcgis.com/share/5ccbb2c7847c48dc9fdf745c8612f785
arcgis-survey123://?itemID=5ccbb2c7847c48dc9fdf745c8612f785
This isn't a Public survey, but you can see how it is constructed. Should get you to the survey as long as it's publically shared. You could also log on to https://survey123.arcgis.com to complete the sharing and collaboration piece.
-Adam Z