For the maths, quite a bit harder than GCSE, and you would just need to work steadily on it from year 12 onwards, ideally you will have good grades at GCSE (e.g. 7-9) but well worth it in terms of university and career options that are possible. The Pearson edexcel textbooks do a step by step approach, with easier worked examples first, so worth taking a peek even on the online version. I have a website - fluentinmaths.com - and in the study area I put some quizzes in algebra, calculus, trigonometry etc which are for people who have studied year 12 but they are 'foundation'/basics for a-level standard. If you take a look you will see what is a good foundation at year 12 but of course, you will not have studied much of it yet, maybe look at the algebra. Hope this helps.