Sending predicted grades to colleges via email

For my UCAS application, my reference did not complete the predicted grades portion, which I know is necessary for Oxford. When I contacted Oxford to ask how to send them my predicted grades via email (as UCAS told me to do) they said to send them to my selected college as soon as possible. However, I submitted an open application, and since this is a time-constrained issue, I do not have time to ask them what to do about that. Do I need to send an email with my predicted grades to every single college that offers my course?

No need to do anything so drastic. You should get a message from the college your application is assigned to, acknowledging your application, shortly after they get it. You can get your referee to send the prediction to them then, once you know which College needs it. Don't worry too much about the timing - as long as your referee gets the prediction to them promptly once you know which College has your application you won't be disadvatnaged. You referee's oversight won't be held against you.