Having gotten into the edging part of Unmentionables, I think the extra 3 balls I ordered are going to be enough. One repeat really doesn't use that much yarn; I doubt it's even a yard2. If all else fails and I come up a little short (and it will be only a little short), I'm going to shrug and leave out a few repeats, which will be reasonably unobtrusive, rather than ordering a whole 'nother ball.
In the meantime I am contemplating another couple of pairs of these, though possibly in CotLin1 rather than Main Line. The CotLin is DK rather than worsted, which will help compensate for the cotton/linen blend being slightly heavier than cotton/wool. I was thinking it might be nice to do a couple in combinations of colors: Swan with Glacier for the waistband and lace edge, or maybe Coffee and Nightfall, or Linen and Moroccan Red in either combination. Cute underwear FTW!
1: This is also the stuff Fire Dragon Year is going to be in when I get over being discouraged by having lost all my notes and work on it again.
2: Slightly later: OK, no, it's a little over a yard. Yes, I knitted a repeat, marked the yarn, ripped out and measured. I'm just like that.