Try putting in 93 octane fuel and run it on the highway for about 30 minutes before retest. The reason is that the higher octane fuel will burn slower and release less hydrocarbons. How high were your NOx readings? From my experience, warmer temps. increase emmissons outputs, so retest on a cool day.

By the way, my 90 Accord has passed emmissons, but failed for rust on the 1/4 panels. I still can't get my car passed.