Hire a lawyer immediately.

Don't negotiate in person. You have to find a lawyer immediately.

Remember how Martha Stewart got into trouble by speaking without first consulting a lawyer.

A lawyer will talk to your boss and ask him/her to provide many documents, in which the lawyer may find some dirty things to sue back your boss. Then you and boss can settle. This is a typical strategy in any Intelligent Property suit. But you can not ask for the documents by yourself.