Maths shouldn't be too hard to get an A* in (70% for Edexcel) if you do all the past papers having learnt the necessary equations and methods (using a channel like Bicen Maths).
Econ will be hard. I got an incredibly high B in my mocks and just hit below an A* for the real thing, even though I put in a lot of effort for revision. Again, it's past papers but exam technique is much more important for Econ. Notably for the 25 markers. Use EconPlusDal for sure, and try to learn examples for each topic. E.g. for monopolies, know about a relevant industry like McDonald's in fast food.