Seriously, don’t panic! I covered the AS content for Chemistry in 3 weeks (I’m doing CIE) and I’m now doing practice exam papers. This is what I did:
1. I sifted through every single page of my chemistry notes that I ever wrote, and selectively took what I thought would be useful.
2. I copied and pasted topic-specific notes from chemguide, and printed them out.
3. I downloaded topic-specific notes from Physics and Maths Tutor and printed them out.
4. I started with the first topic, and read all content that I had either written notes on or got from the above 2 websites, highlighting key definitions, concepts etc in 4 different colours.
5. When I finished reading the topic, I put away all of my notes on that topic into a subject-specific folder.
6. I repeated the above for all topics in Physical and Inorganic chemistry. It took me 2 weeks to do this.
7. I then printed out notes for organic chemistry, read through them, highlighted key points etc and then put them away into the same folder.
8. An additional thing that I did for organic was to create charts for the reaction pathways and mechanisms, so definitely do this because it will make it infinitely easier for you to keep track of all the reactions and understand how they are linked.
9. Starting with the 2004 exam paper, finish each and every exam paper until 2017.
You can easily do 6 exam papers a day, so you should aim to set aside around 10 days just to do chemistry AS past papers. That is 60 exam papers in total, which will give you more than enough experience to get an A.
Good luck!