Are you sure while importing you have selected the correct Basic notetype? What you have described is not the basic, Basic consists of only two fields: {{Front}} and {{Back}}
Thank you for your response and clarification regarding the Basic note type having only two fields (Front and Back). I was wondering if it’s possible to use a custom note type in Anki with additional fields (e.g., Front, Back, and Extra).
If yes, could you guide me on how to configure Sheets2Anki to map multiple columns from my Google Sheets file to these additional fields?
You don’t need to use an addon. You can directly import a csv file. When you import, there will be an option to select the Notetype you wish to import to and what column maps to what field. Read this to learn more.