Hi Kieran,
Glad you found a solution, thank you for updating this post!
If you get duplicates again, try these steps: while only logged into one google account (very important) try and reset the trigger, open up docAppender, click through until you get to Step 4, then you should see a 'disable' button the bottom of the sidebar.
Click disable> refresh your form>open docAppender and go through the set-up again then try a test submission.
Thanks!!