Knitting with eyelash yarn

[Flossyfloof]

Helllloooo!
I want to knit a shoulder wrap/capelet using eyelash yarn. I am imagining basically knitting an oblong with a nice big ribbon to draw it together. I know from experience though that once knitted eyelash yarn items fan out at the ends, like trumpets. I don't want this to happen! Please does anyone have a top tip? I am thinking maybe cast on and immediately create stitches - but I have no idea as to ratio...
Thanks!

[MuffinPaws]

Could you knit it along with another fine yarn like Shetland one ply?