During my 7th month of pregnancy i sniffed few drops of gasoline for few days.. could that be harmful to the baby?

Unlikely : Sniffing gas is not healthy. I would recommend you stop doing that.

Baby filtration: As long as you were not huffing / bagging (or intentionally inhaling gas fumes for an extended period of time), then small / passing exposures to usual urban environmental smells should be handily addressed by your protection systems (lungs / liver / etc.).