It’s just a scarflet, so exact gauge isn’t that important for this project: use the suggested needle and you’ll be fine. You’ll use much less than the full ball of Malabrigo -- I used about half of one.

(As some have pointed out, the scarf is technically knit in half-linen stitch, not linen stitch…but calling it the “half-linen stitch scarflet” just sounds weird to me. So there you have it.)