The message is probably gone if it was pretty old. But, just in case, you may want to try and check your "recently deleted mail" folder. I didn't understand whether this was mail that you sent originally or was sent to you.
If you sent it originally, you can also check to see if the mail is in your Sent mail folder. It may still be there.
If it was sent to you, you can also check your Old Mail folder, or as a last resort try to have the sender resend it to you.