If you enjoy maths, you will find the A-level relatively easy.
If you don't really enjoy maths that much, you will find it requires a lot of work.
Luckily, I enjoy maths.
Also, as others have said, do the further maths A-level as well. Makes the standard A-level a lot easier, and is crucial for getting into a good Uni for Maths. Studying the STEP papers is also a very good idea.
Yeah I forgot to mention that, I love maths, not when it's complicated but I always keep trying. It's by far my favourite lesson.