Undeserved Job Offer...What should I do?

I interviewed for an office job with the local government of the state I reside in. I DID NOT feel that the interview went well at all however I fear that the employer feels obligated to hire me as a result of my service in the military, or perhaps not many others had been interviewed for the position. I am afraid that I am unqualified for the position as it involves secretary work for supposed higher ranking individuals. I do need the money, however. What should I do?