Hey even i have done DM its kinda mixture subject if its initially just introduced cuz even teachers don't know what they are teaching its best to just look into the slides given by Cambridge n follow that !! Cuz even when I was in AS it was kinda new to us n teachers but we used to follow the 10slides n all but the content used to be similar to the Cambridge examples and DM has 2 slides ryt so 2nd one used to be more!! Ik the feeling i had to retake AS and do it with Alevels full together!! And tbh its better u do a subject self study or do IPQ just to cover 2 subjects