Please check this sentence grammatically and punctuation wise, and see if it is proper. If not, please correct.
Macbeth seems confused and asks if the omen told by the witches is good then why does it also suggests a heinous deed "whose horrid image doth unfix my hair/ And make my seated heart knock at my ribs".
(my doubts is about using "my" [first person possesive form] quoted from the original text, with a sentence of a 3rd person subject) I hope you get what I mean.
To begin with, the word "omen" seems incorrect, and the word "told" seems unnecessary. The witches utter prophecies which Macbeth describes as "supernatural soliciting." I think you could delete the word "heinous," since Macbeth says the deed has a "horrid image." As far as the word "my" is concerned, it may seem a little awkward because you haven't shown that you are going to quote him. So, the sentence might be better if written as follows:
Macbeth is confused and asks himself if the "supernatural soliciting" by the witches is good, then why does it suggest, as he puts it, committing a deed "whose horrid image doth unfix my hair / And makes my seated heart knock at my ribs / Against the use of nature?"
I hope this is helpful. I have tried not to change your own sentence too radically.