Editing a Public Sheet

Editing a Public Sheet

I created a sheet and marked it as public because I wanted to send about 100 people the link, and let them click on it, make changes and hit save. (It's a sign-up sheet for a teacher appreciation breakfast.) But I find when I follow the link myself, without logging into Zoho, I am not allowed to save my changes. Is there any way to use Zoho to do what I want to do? Or will anyone who wants to edit the sheet have to be invited using "share"? Will they have to join Zoho and log in themselves?