It said he knew there was mass cheating about people collaborating in group chats and to confess and you will be looked at more favorably by him and the dean.

How would he know this? The answer is, he doesn't. I promise you this, whether or not you confess, the punishment will be the same. You won't get any pity for it.

So am I too paranoid that I’m going to get caught?

If you were dumb enough to upload a question on Chegg in the middle of an exam, and if there's any personal information on your account, then yes, there's a pretty good chance you'll get caught. It's one thing to collaborate with people you trust, it's another to upload the question to a public website that's linked to your email address, name, and school. As part of an official investigation, Chegg will release that info to your school if it requests it.

Now that being said, there's a chance your school still hasn't found out about the uploaded question yet. The best thing you can do now is change your name, email address, and school name associated with your account, and then call them and ask for an account and data deletion.