I think I messed up. I wanted to email each of my colleges about the chance that there’s an error on my transcript, namely one of my trimester classes may not have shown up in the midyear report but will for sure in the final report. I stupidly bunched up all 8 of my colleges as recipients of this email, and after sending it, now they can all see the other colleges I sent the email to. Will this hurt me?
Adding to above, is there anything I can do about it?
I don’t think there is anything you can do about it now. It is a simple mistake and colleges realize that applicants apply to multiple schools. Don’t worry too much about it.
I hope so 
Should I send each college another email with the same content, but also telling them to forget about the former one?
What’s done is done, and a follow up email would only make it worse. I wouldn’t have done it like that, but I doubt it’ll affect your chances. They know you’re applying to multiple colleges.
I agree with elliebham. What’s done is done. No need to draw more attention to it. They may not even notice and if they do, there really isn’t anything you can do about it. And all colleges know that you aren’t just applying to their school.
As busy as admissions officers are, he/she may not even notice your error. Sending a follow-up email will only point out this mistake.
It depends what the eight schools are. If, for example, it were all eight of the Ivies, that could (probably won’t, but may) work against you. You should be fine.