creating a bootable USB

Hi all,

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So i'm currently trying to duel boot mac OS High sierra and windows 10, windows 10 is on my C drive and i've created a 400gb partition on my D drive for mac OS. I'm trying to create a bootable USB with Rufus but it's saying "failed to scan image"

note: the copy of high sierra is 5.3gb so FAT 32 wont work, is there a prefreble format?

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I have two questions:

1. am i going about putting Mac OS on my laptop right
2. am i missing somthing with mounting the image