Write down the errors you have found in the appraisal report. Give your error report to your lender. If the errors have an effect on the appraised value, your lender should forward your found errors to the appraisal company/appraiser for a re-evaluation.

Obviously the appraiser got it wrong when he compared it to the wrong community. You can either appeal it or if you want, stick with it and try to renegotiate with the seller. I believe that if you want this house however, and not to upset the seller, appeal and have it re-appraised.