Yes, imo past papers are the best revision method, even if you are behind on the content. However, simply mindlessly doing past papers isn't really enough, you have to make sure that you are thoroughly marking the papers and analysing your mistakes in them (not just mentally, you have to actually write down why you made the mistake), as well as relearning any content gaps.
You also need to be prepared to be faced with not-so-amazing results at first, but that's a good thing, since it pretty much tells you all of your actual content gaps and makes it much quicker to revise through them efficiently and focus on your weak areas.