Numbers never lie / math is infallible

I'm knitting. That's nothing new, of course; what a silly thing to say (write, err type).

I'm knitting the Leah Tunic from Purl Bee, or rather, a modified version of Leah. I don't like the untidy hem of the original Leah, so I'm using a deep garter stitch border at the hem. I'm also shortening from the tunic length so that the bottom hits right below the waistband of my jeans.

I've also substituted in a yarn with a significantly tighter gauge than called for in the pattern: 8.6 sts/in rather than 7 sts/in. The yarn is a new 100% silk lace ribbon yarn from Karabella called Manipur. More on that later.

After doing body measurements, gauge swatches, and a bunch of calculations, I cast on the required number of stitches for the middle size - even though the numbers said to cast on for the larger size.

I am now done with the first skein of Manipur and a few rounds past the second decrease round. I can now take some kind of semi-accurate measurement of the piece. As expected, 14 inches across for a circumference of 28 inches. I want/need it to be 15 inches across/30 inches around.

Umm, yeah. Why am I surprised? The gauge swatch, measurements, calculations - all indicated that with the medium size number of stitches, the piece would measure about 13.9 inches across (circumference 27.8 inches). Numbers never lie. Math is infallible. Why, oh why did I cast on 119 sts (each for front & back pieces, total 238 sts) rather than 130 (260 total)?!? I am an idiot, that's why.

So now I'm faced with a dilemma. Do I keep going, figure out a way to compensate for mistake, and hope for the best? Or do I grit my teeth, kick myself in the ass, frog and reknit?

I think I may have to go with the latter option, much as the prospect pains me... Because Manipur is a drapey silk that wouldn't look so great with negative (or in this case, borderline super negative) ease.

Oh, and for the record, Manipur is a great yarn to work with (minus the twisting, but that's to be expected with ribbon-y yarns), but a nightmare to wind. The skein is about 2 feet around, which makes it impossible to fit onto my swift. Oh, and it tangles like no other. I am SO not looking forward to winding anymore skeins of the stuff! Then again, I might prefer even that to frogging and reknitting :oP