Something else just occurred to me, though it sorta falls into that "Is it plugged in?" category. But it occurs to me that with a scarf, checking gauge isn't all that important, so you might've skipped that step. But when you're trying to get something to be a certain size, you can't really do that. The pattern you're using will say 108 stitches, but that's predicated on a certain number of stitches per inch, and if you knit tighter or looser than that 108 stitches for you won't be the same size as 108 stitches for somebody else, given the same yarn and needle size. And the variations can be significant. (A lot more than you'd think.)
So you want to knit a swatch using the yarn you're going to make the thing out of, measure 4 inches and count the number of stitches you put into those 4 inches. Ideally you'll measure it in 3 or 4 different places and take an average (especially if you're just getting used to DPNs). For the sake of completeness, you'll usually check the number of rows (or rounds, in this case) in 4 inches, but that's probably as critical for this project.
Also, when the work is still on the needles, it's GOING to look smaller than it actually is. On the needles, your stitches are turned so they're perpendicular to the needle. Once they're OFF the needle, they're gong to rotate so they're in the plane of the fabric. And that's going to make the piece a LOT bigger (maybe as much as double, depending on the yarn/gauge).