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To fix that, you can simply undo your changes or add back the missing column, you need to set the column name the same with the name of the field where it is associated with.
However, I strongly suggest that it would be best to remove the integration then re-integrate Google Spreadsheet again, please note that it will create a new spreadsheet and will automatically be populated with all of your form's existing submissions. The old spreadsheet will remain in your Google Drive but will no longer receive updates.
Personally, I do not recommend editing or making a lot of changes on the spreadsheet that is integrated to your form, edits or changes might break the integration or stop it from updating. I suggest that you use another sheet or spreadsheet and use a function or formula to reference from the master sheet/spreadsheet. Example function is the IMPORTRANGE, it automatically copies or refers the data from one spreadsheet to another. Here's an article about it: https://support.google.com/docs/answer/3093340?hl=en. With that, you do not necessarily need to make changes on the integrated spreadsheet.
I hope that helps.