We cannot store more than 2 million cells. This limit is given to us by Google and affects not only our add-on but all other add-ons alike. If you subscribe to our service, then there is nothing we can do to give you more cells. Sorry!
Please raise this problem against Google. If you want to sign the petition to increase this limit, please add your comment below this article.
As a workaround, please try to remove any unused and blank cells within the spreadsheet.