Your CO2 reading should be no more than 3.50, since yours is a cat model they'll be looking at you HydroCarbons which the cat is ment to reduce.
If you can achieve close to 0.20% vol on CO and 130ppm (parts per million) of HC then you'll be healthy. There isn't a great deal of difference between the test figures for the cat and non cat models. So don't worry about it as long as you don't overfill with oil or have a dirty air filter it should fly right through.
One other point; i can't remember exactly which date/year it was but vehicles manufactured before that date can legally have thier cats removed as they were not manditory before that date. Check it out on the vosa or government websites.
