I was in a hurry to get to the airport and accidentally put 14.8 litres of Shell Fuelsave Petrol in my 2006, 56 model diesel BMW 520d SE Auto. At the advice of an old man who happened to be at the forecourt, I put in 500ml of Shell Helix HX5 15-W-40 engine oil into the tank and brimmed it to the full with Shell Fuelsave diesel and drove to the airport, 50 miles away. On my return, I drove back and when tank became half full, filled up with BP Ultimate diesel and 60 mls of Millers Diesel Ecomax. The car has now run a total of 300 miles since the incident but I am a worried man and have a few questions:

1. Could I have done some lasting damage to the car? Now that I have done 300 miles plus, is damage still possible? Car seems to be running fine.
2. I have so far done only 45k miles in this car. Is it prudent to keep it for the long term?
3. If I am topping up with BP Ultimate do I need to put in Millers Diesel Ecomax as it already has a high cetane rating?
4. Is Millers Ecomax a good lubricant? Should I be using something else?
5. Should I be doing something else?