Each recipe has "Personal Notes" that the recipe contributor adds - it can be something about extra ways to prepare the recipe, or more often a story about the recipe.
The "Add to Story" is really for others in the group to add comments on recipe. The recipe contributor should only add comments on "Personal Notes" of a recipe (edit the recipe to get to that field).
To edit the "Add to the Story" go the recipe view (not edit) and at the bottom of the recipe, you'll see the story additions. Click the "Edit" button next to any of your comments. Make your changes. Then save.
To edit personal notes, EDIT the recipe and add the same comment under Personal Notes and save.
You can also globally just turn off/not include any of the Add to the Story comments from your printed book. Go to Layout & Design, Select Recipe Layout. Scroll down to the "Long form recipe options" box. Uncheck "Include comments and stories from all users added (in addition to the comments in the recipe)" and save.