I'm making an alpine stitch neck warmer (flat), but I didn't make it long enough. How can I make it a bit bigger before sewing it?

Alpine stitch, 66 stitches across. Well, I didn't swatch. So this men's neck warmer isn't big enough to fit a an adults neck. I'm crocheting it flat and am going to sew it up at the end. I'm about halfway through. How can I add width in a subtle way? I would like to avoid a visible seam of possible.

Worsted weight yarn (Symfonie Yarn Bella), and size G hook.