Petrol in diesel fuel tank - what should I do?

[Observer]

I stupidly picked up the wrong fuel hose filling my Merc turbo-diesel this morning. Put in 4.5 litres petrol (65 litre tank) before I realised the mistake. I then topped off the tank with diesel and have driven home approx. 3 miles. What should I do now?

Am I right in thinking the petrol will float on top of the diesel and that the fuel pump will draw reasonably clean diesel from the bottom of the tank as long as there is plenty of fuel?

Will the petrol slowly mix with the diesel or do I need to take the car to have the tank emptied or similar?

If so, would it be OK to drive or do I need a transporter?

The car has 115 thousand miles on the clock so I don't have to worry about invalidating a warranty. I just want the easiest and cheapest solution.

Thanks in advance for any advice.