Temperatures of 100F are not a reason to smell gasoline fumes in the vehicle.

Sport mode has nothing to do with it.

Overfilling the tank can cause this, since fuel is cool when it is stored underground and expands when it is in a tank in a higher ambient, but if you haven't just filled it that shouldn't be an issue.

Evaporative emissions (fumes from the tank) are a controlled emission, meaning that the vehicle has a vent system and charcoal canister designed to take in those fumes and not let them get to atmosphere. If that system isn't functioning correctly, or if there is a small leak somewhere in the fuel supply lines to the engine, you could have an odor of gas fumes.

If you continue to smell gas fumes, suggest you determine exactly when and how it happens, ie parked overnight in an enclosed space, or whatever. Then ask your dealer to replicate those conditions, at the dealership. At this point you aren't trying to diagnose it, you are trying to replicate the problem. Your goal is to have the dealer service manager nod and say yes, I smell it too. It isn't relevant that they haven't found a problem, if there is a problem they just haven't found it yet. The first step is to get them to agree that there is a problem.

It is possible that it isn't a gasoline smell. You have a new vehicle, and there are numerous things that get hot and burn off in the first short period of ownership, entirely normally. Some of those could be confused with a gasoline smell. Not saying you don't know what you are smelling, just that there are other possibilities.

Good luck, and let us know how it works out.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue