I'm doing the OCR MEI spec, but they're all pretty similar. I am not 100% sure it will be the same for your year because of changes to A Levels (so speak to your teachers about it), but it's a modular course, meaning you sit exams for different modules that cover different topics.
Core modules are essentially 'algebra' - they are mainly Calculus and Trigonometry, but also lots of other maths stuff - 'pure maths'. My A Level consists of 4 core modules.
Stats modules are bs because stats is ugly horrible number crunching stupid stuff with some probability work thrown in (which imo is actually very nice maths). Fortunately, only 1 module is part of my A Level.
Mech modules are nice - they're applied maths, but a lot nicer than stats, and they're really helpful (practically integral to) engineering, and very helpful for Physics A Level too (there's a mechanics module in that). The maths you do involves forces and everything that follows on from that. It's fun, and easy once you grasp what's actually happening.
There are a few other module types, but you're unlikely to do them in A2 Maths. I'd say choose it - it's great fun, and shouldn't be hard if you're at all good at maths