Good luck for your A2s. However you should understand getting an A* is hard, because 90% in the A2 modules is alot harder than 90% in the AS modules However the A* grade is irrelevant of what you got in AS level (as long as you get a B or above).
Just to illustrate its difficulty
In my final maths exam I need a U to get an A overall
but an A* to get an A* overall!!
What should I do?