It's hard to change something.
About 2 years ago, I went to a new teacher. He is a brilliant teacher, but one of the first things he noted in my playing was that my embouchure was all wrong. I was taught the "smile" embouchure which just spreads the airstream instead of creating a focussed one.
It's taking a lot of practise, and perseverance on both mine and my teachers part but the difference has been amazing in my sound (with some help also Trevor Wyes Tone exercises!.)
If you trust your flute teacher, keep trying.
HELP WITH EMBOUCHURE
Moderators: Classitar, pied_piper, Phineas