Question: what is banquo worried about at the beginning of act 3?
Answer: At the beginning of Act III, Banquo recalls the prophecy of the three witches and wonders how it has all come true for Macbeth. He remembers that the witches told Macbeth that he would be the Thane of both Cawdor and Glamis and eventually the king and this has come true by this point in the play.