I just put ~11 liters of Petrol in a Audi Q7 2008 with a tank capacity of 80l, I immediately filled it up with diesel and drove about 10 km to my hotel. Some sources say it’s fine if I keep topping it up, others say I’m screwed. Am I ok? Should I add oil?
Your Q7 has the common rail fuel system. That fuel system is VERY VERY weak and is highly susceptible to damage from misfueling.
The general consensus is that anything more than 2% contamination has a high risk of high pressure fuel pump destruction.
11 liters of an 80 liter tank is 13%. Do not drive your vehicle again. You need to drain the fuel tank and all of the fuel lines, flush them completely with diesel and a fuel lubricant improver, then pray to what ever diety you believe in.