I've had a number of E420s fail emissions test over the years, and it was always cured by a bottle of "Guaranteed to Pass", following the directions, followed by new spark plugs and a warm engine for the test. I've never heard of an E420 catalytic converter failure. But in any case post your test results in the morning.

Also try reading the emission fault codes on the 8 pin connector in the engine compartment - no tools required.