I’m in the same position as you; self teaching and my school will try to find a prelim. I’ve done AH maths and I wouldn’t say you’re at a disadvantage since there’s no overlap at all (there is some integration involved in a minor part of the course, but it’s all covered in Higher). I’m studying from the Maths in Action textbooks (Statistics 1 and 2) and there are 8 units covered; Probability, Random Variables, Sampling, Hypothesis Testing, Control Charts, Hypothesis Testing 2, Students’ t distribution and Linear models. I’d say that random variables, sampling and hypothesis testing 1 would be present in the prelim for sure since the other units all follow on from knowledge from those.
The statistics 1 book is expensive on eBay (if you don’t already have it) but I managed to find some notes that are similar (but not the same):
https://www.national5maths.co.uk/wp-content/uploads/2016/04/Stats-unit-1-course-notes-7852math2_tcm4-123857.pdfHere are some notes which I haven’t checked out yet, but I intend to:
https://www.tes.com/teaching-resource/ah-statistics-course-notes-12263633One word of caution, the textbooks may not quite cover everything necessary, so refer to the course specification to see what else you need to learn (there isn’t much, and it’s all really easy).