Screechy high notes on the flute?

While playing the flute, my sister heard how I was playing and she remarked that while I was playing the notes of the highest octave (B flat - F), they were quite screechy and unpleasant sounding. I haven't thought of this nor have I noticed that I was playing the highest octave so wretchedly (I havent heard another flute player play in half a year and I dont have my old band director who was a flute player to teach me anymore). So I was wondering what is the proper embouchure to play the highest notes correctly? Thanks in advance.