advice on A level Edexcel Maths ,AQA chemistry and OCR computer science revision

hiya!
i can only help with the maths really and kinda computing but i do AQA instead. dont know how it works for your school but my school gave me tasks to complete before entering sixth form to make sure i was ready. for maths i would say find the textbook online (a level edexcel maths pure year 1) and doing some reading if the first few chapters, and making sure you're all good with anything that is an extension of gcse maths, for computing, look up project euler and try a few of those problems - they're really good for making you think and forcing your code to be efficient to actually work. any coding practice is good practice, but yea project euler is a good place to start.
let me know if you have any questions,
lily