How do I make cron email my @gmail account

It would appear that you have configured smtp.gmail.com as your smarthost for the mail server. You need to remove the smarthost configuration or edit it so that your server is at all capable of sending mail to the outside world.

The configuration you have now for the mail forward appears to be working, but is failing because smtp.gmail.com is rejecting the mail.

Update: For future reference, the problem was in /etc/mailname which listed a name that wasn't in the mydestinations list of postfix. This caused all mails to be considered foreign and the mail bypassed /etc/aliases processing.

Solution extracted from question

(thanks to Ressu)

The problem was with the file /etc/mailname

This file was created by the Ubuntu installer and contained the wrong server-name. Once I changed it to match "ricardo-laptop" postfix realized the emails were intended for local delivery and started to follow the aliases