It will be fine a 3l of petrol in a tank of diesel is perfectly fine it will act as a anti gel agent in cold weather. 11l is a bit much and will essentially float on the diesel, so your car will run fine until you get low in fuel.
The petrol acts as a solvent and thins the lubricants in the diesel, so the engine runs hotter.
So fill up at 1/2 a tank and run a few tanks through it and you will be fine.
It will be fine a 3l of petrol in a tank of diesel is perfectly fine it will act as a anti gel agent in cold weather. 11l is a bit much and will essentially float on the diesel, so your car will run fine until you get low in fuel.
The petrol acts as a solvent and thins the lubricants in the diesel, so the engine runs hotter.
So fill up at 1/2 a tank and run a few tanks through it and you will be fine.