Definitely not worth repeating 1/2. The minimum requirement for 1/2's is an S.
If you aren't confident due to the content in the 1/2, I would take the advice from the poster above and perhaps spend some extra time revisiting it or seeking out a tutor who can work through these concepts with you.
If you aren't doing well in Methods, I'd be looking into why you have chosen it also. Is it due to a university pre-requisite? Is the aim for it to scale up so you get a better ATAR? Did you choose it just 'because'? If it isn't absolutely necessary to your success and you aren't doing well despite efforts, it may be worth considering General and aiming to do better in that. Any decision you make surrounding subjects should go through a Careers Counsellor at your school first as they are (in most cases) well informed to advise on any ramifications.