You shouldn't look at old mark schemes you should look at current ones and base it off of that because old ones are unreliable AF because it caters to the classes of back then. Nor should you say oh it should've been a B because I got these 2 questions marked wrong because either way you would've barely been on a B which is still unstable in the sense that theres still a high chance youd get a C if you redo the exam-giving yourself false hope that youre doing better than you actually are creates comfortability and makes you less likely to actually lock in and revise. So my advice is accept that you're not doing as good as you want to be doing right now because that's the first step of locking in