Wow. Those attorneys! They are always to blame, ha? Where were you looking when you signed that application? The other way?
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: firstname.lastname@example.org; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.
I concur with Mr. Tasoff. Bring a corrected copy of the affidavit to the interview. I also agree with Mr. Segal that you do have a duty to review whatever you sign carefully. Fortunately, you did eventually catch the error and are now taking prompt steps to rectify it. Under these circumstances I doubt any damage has been done.