In response to your first question, it depends on your school but most schools use the last years papers as they are locked so students can’t access them easily.
In response to the second question, i don’t know which subjects you take or specifications you have so I can’t help you much. However I would advise you to revise to the best of your ability and treat it like you would a real GCSE because mocks are really good preparation for GCSE and a good indicator for where you are currently at. I would advise going through the specification for each of your subjects and seeing if anything looks like it may be difficult or you haven’t covered and revising or going over that.