I’ve driven well over a thousand miles this week for nothing but pleasure, in a car which is useless for anything else.
I think you can rest easy. 1,000 miles at 40mpg means you produced 276Kg of CO2. That's about a half of Boris Johnson used when he took a private jet (A321) from London down to Cornwall. (based on a average of 250Kg/hour for jet transport).
I bet you also did a great deal in your week's holiday to assist the UK economy.