If you do turn the domain name over to the company, you should probably state in your correspondence with them that in doing so you’re not admitting to any wrongdoing on your part, and you should probably have something in writing from them indicating that they won’t take any action against you in the future.
Please keep in mind that I’m not a lawyer, and this isn’t to be misconstrued as legal advice. It’s just common sense, in my mind.
And I would recommend contacting a lawyer immediately IF they have a lawyer contact you.