It doesn't make sense to talk about an A* in a module or in AS or A2 individually. An A* is awarded for the whole A-level. For most subjects, you get an A* if you get an A overall, but 90% average across A2. For Maths, an A* is awarded if you get an A overall and a 90% average across C3 and C4. For Further Maths, an A* is awarded if you get an A overall and 90% average across your best three A2 modules (since you can get a Further Maths A-level with, say, 2 AS and 4 A2 modules, rather than a 3/3 split).
It doesn't matter what your individual module scores are, or what your AS result is, as long as the above conditions are met.