If you spilled some of the gas into the opening of the fuel door area, the black boot may have been leaking a little. This boot keeps fuel from spilling into the trunk if an overflow happens. I would check the boot and the fuel cap seal.

This happened to my sister in her 300 e and it was the cap, it was not installed correctly (duhh).

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS