Hi Clare,
Its highly unlikely that you have damaged your engine, unless youve ragged it from cold or done thousands of short journeys in your clio. Oil will age a lot quicker under these circumstances than it would if the engine was running all the time. I know a taxi driver that changes his oil every 30,000 miles becuause the engine is always running and up to temperature, his 406 diesel has done in excess of 250,000 miles on the same engine !
Most diesel engines need a diesel oil becuase this is designed to cope better with the acids produced as a result of diesel combustion. The castrol GTD oil should be fine but check it meets the standard required for your engine first (car hand book). If you take your oil into a renault garage they will charge you about £35 to change it and fit a new oil filter at the same time. Just make sure you ask for the container back so they dont put standard oil in your car and keep the good oil for themselves !
stu