I've heard that topping off the tank is a way to destroy the activated carbon canister filter on BMW's, and will result in the tank not being able to properly vent cleanly. Check all the vent hoses to the canister filter and make sure they are connected, but first, re-check all your fuel hoses for leaks. I'd park the car outside until it was fixed, one spark with concentrated fumes in your garage will spell disaster for your whole family. Get it checked PDQ.