1.Once you send a mail, you cannot recall it or 'Un send it'. Sorry, you cannot rectify it.
2. For future use, if you want to be safe, you can buy some time only 30 seconds of undo time. Even this is not fail safe as in reality, the sending of the mail is delayed by 30 seconds.
Open your gmail account.
Click on the setttings wheel icon in the right top corner
enable the undo send, you can do it for 5- 30 seconds only.
then save the setting changes.
3. As long as it is not an attested copies, there should not be a problem.
4.You can message the sender with a recall request and to delete the sent mail with attachments. I would suggest typing a disclaimer that data for unintended recipients would be invalid and it cannot be used by other parties.
5. Be on the look out for any unusual activity related to the documents.