Hi there,
I take advanced higher maths in Scotland and let me tell you I was like a 100% maths student at National 5 and Higher level. Advanced higher is hard but it’s primarily silly mistakes that get me as well since my techniques are pretty much there in my head. I think for me it’s just knowing that I have the techniques puts me at ease but then the time pressure is stressful.
What I do is really go through even the most simple arithmetic—don’t be too overconfident or quick as I feel like that’s where the silly mistakes can come from—but then balancing that with timing. Personally, I don’t think there’s really a set way to “train” that, although someone else might think differently. I think it’s just when doing questions to maybe really think about all parts of it, even those easy parts, because it’s normally those easy parts that you overlook that can come and bite you in the end.