Welcome to the CPL Navigation question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.
If you set up your computer with a flight planned track of 330°M and a wind of 090°M at 20kt you get a heading of 337°M The computer pays 338°M as the correct answer. I don't know how your computer has 331°M as the correct answer.