Don't panic. First of all, you can use the car. Before wasting time at dealer, do a manual 'reset' with the car at full operating temperature on a level surface while idling; that's going to give you a proper reading, not the one the car gets on its own about 10 miles into your trip. And even if the reading is high, it's probably going to be 1/4-qt at most, which does nothing to your engine. And it's easily remedied by draining the front oil sump. The TWS oil is very expensiive, and it's not like a tech is going to throw 10 quarts in there. If it's indeed 'overfilled', it happens when oil is not allow to drain sufficiently, so tech puts the 8.8 liters called out on the manual, and ends up a bit overfilled. Nothing to worry about, but it's a sensor, and if it gets to that level it'll throw that message. It's not like a 1/4 of a quart is going to fry your engine, but BMW does a good job of scaring you into that
. Just take it in when you have a chance if it reads high when reset like explained above. Or drain the front sump and be done with it
If you want to better understand how the darn sensor works, do a search. Take care.