have i fixed my high emissions?

My emmisions were 0.596% co2 -fail, HO and Lambder checked out. I was told by a mechenic this was probably down to the EGR valve. I did some research, apparently, taking of the valve and making an aluminium blank to block the effects of the valve is suppose to reduce co2. I tried this method, cant do any harm car seems to be running nicely but i wont know till it goes on the diagnostic. Any advice from anyone would be appreciated.