If you're at AS of course there is time to revise.
A2 is a similar case.
The step up from GCSE as you probs know is HUGE. I went from A*AAB to CCEU in my first mocks in AS. it's purely practise that makes you better. there's always time to revise.
The step up from AS to A2 is also very large, not as much from GCSE to AS but it's still big,again i went from BBD to CFU (AS to A2) and i know it's just time before they go back to normal.
basically just revise like normal, don't worry too much about your grades, you will naturally learn how to answer the questions right in the correct way, trust me