You don't have to worry. Flipsnack offers an auto-draft feature, so all your edits and settings will be saved as draft even if you did not publish your changes.
If you saved a flipbook as draft and decide you don't want to keep the changes anymore and return to the last published version, simply click on the 3 dots on the right side of the flipbook labeled as draft and select Discard draft.
You can read more about the flipbook labels here.
The last version of your flipbook will always be in My Flipbooks.
Important: To save the text you edited, simply click anywhere on the flipbook or outside of it in the gray area before proceeding with other edits.