So I just applied to some of my colleges on Common App a few days ago, but I just realized that I listed some of my activities and details on my Common App profile incorrectly. Would I still be able to make changes to my profile, and if I can, will the changes be seen by the colleges I already applied to?
Yes, you can make changes, but No, those changes will not be seen by colleges to which you have already submitted your app.
You can email colleges with changes/updates, but think carefully before doing that. IMO Only send changes if it’s some critical information that needs to be corrected.
Advice above is spot on in all regards. There is a preview button that permits you to review each section of the app. Use it to make sure the app is exactly as you’d like it before submitting it to schools you have yet to submit your application to.