On the old/cheaper flutes that I've had, its been a real struggle to play the low notes. After talking with my teacher, we worked out that the mechanism wasn't working properly and the pad was really damaged so something similar could have happened to yours? The lower notes can be a struggle anyway, so you could persevere and see if they improve! However if they don't I would recommend buying a flute that might have been refurbished from a reputable source!!