If the oil level is just low and your not ready for an oil change just buy a quart of oil from the dealer and add it. I'd just call ahead and ask if you can come in and buy a quart to top off your oil. The reason why I would call ahead is the M3 uses 10w60 while non-Ms use the standard 5w30 so they may not always have enough of the 10w60 on hand at the service department.
When I went in they had to bring some over from the parts dept. After that I ended up just buying a few extra quarts on my own from Tischer that way you always have some on hand.