Export your document as a .xlsx file saved to your computer.
Open a new email in your gmail account.
Address and compose the message,
Click the Attachment button.
Navigate to where you saved the file and double click the file name.
the navigation window will close and you will be returned to the compose screen showing you message with the file attached,
Send the email.
Notes:
When you Export a pages file to a different format, Pages creates a copy of the file, translates that copy into the named format (.docx}, saves the translated file to the location you specified, and discards the 'in memory' copy of the translated file.
The process makes NO changes to the .pages copy of the document currently open in Pages.
If you re-open the .docx file (in Pages), Pages reads the .docx file, translates it into a .pages file, and loads the .pages version into Pages for editing or reading. NO change is made to the .docx version unless you edit the document then export it to the .docx format and save it in the same location and with the same name as it had before.
Regards,
Barry