From someone who got very high marks in A level econ, use the tutor2u website and booklets! They give you all the knowledge and resources you need for the exam, Their guides may be too detailed as they go into context and talk about many things which have actually happened in the world over these past few years but the way I see it the more you know about economics (theory and context) the better you will do. Also practice makes perfect so practice as many past paper questions as you can, try to get full marks in all of the non-25 markers as they are fairly easy if you know your content which allows you to have some room for error in the essay, which you can still easily get 15-20 marks on if you practice/know the exam technique for it.
Also as you are doing aqa, unit 2 and unit 4 are almost identical in my opinion, so even if you didn't do well this year I would recommend retaking it next year because you won't need to revise for it as much as you did this year (as you would have already covered the content by going through unit 4).