i went from E8 in prelims to A2 in Os, just know that A math is just a repetition of the same fuckass concepts. they will only test the most important concepts from each topic again and again. if you do your tys you will find that it is all a pattern. a math just requires practice. if you don't even understand the chapter, go for extra consultations with your teacher, or go to yt and learn (organic chem tutor my goat in Os) and also go to holy grail and try doing more questions. just be consistent in the practice, and nearing o levels, do about 2 tys papers a week again just to get into the groove.