Just had my car tested and my CO % Vol is 6.64% and for an MOT it should be 3.5%?

Now a few questions...

1) is this level damaging to my engine?
2) is that why my fuel bill is so bad?
3) will i be losing power?
4) what can i do to fix it?
5) what would you charge me to fix it? / tune it?

Someone was telling me today that this would cause bore wash and bugger my engine ?

Cheers

Paul

PS this was setup by a compnay near me and i've had a miss fire and overfueling since then.