I was recently told by BMW Australia, you can overfill up to a litre or two, and even with the on-board warning, should not harm the engine. The /// cars - 3, 5 and 6 - are having the problem of not registering the correct fill level, and dealers are topping up more than that's required. When the customer drives away, and after a few kms the warning comes on saying too high. So it's ok. Unless you added about 4 litres on top of your 8.8 litres.
E92 M3 2007 - ///PE with Test Pipes and BPM Stage II; CF Interior & Splitters; CIC with Connected Drive