This is why it's a good idea to not only make a tension square or swatch, but to wash and dry it and measure it again, to see what the fabric will do after washing.
That's the same green top sitting underneath.
The significant widthways growth is fine with me, since I planned for it and the fit is good. I learned some lessons with this yarn last time, when I made a different cowl-neck top with it: 1. Slinky yarn with no memory looks and feels better with positive ease (so it can drape) rather than stretched tight. 2. Stocking stitch fabric made from this stuff grows quite a bit in width.
Funnily enough, because of the lack of ease in that earlier Coachella top, I didn't learn a third lesson that would have been handy - given a chance, the fabric does grow longer too. I actually knit this a bit too long because I thought from that past experience that it would lose a little in length after washing. That may be true in a relatively small swatch/tension square (and here is where swatching can really let you down), and it happened with the other top that was a bit too tight, so in stretching around me it tended to pull up. This time I made sure there was a decent amount of drape, it sagged way down.
It's wearable; I wore it all day on Sunday. But it is really too long (I tucked the ribbing under because it looked bad stretched over my jeans and hips), and the sleeves/armholes are too long as well, they look a bit funny proportionally. I've decided it's worth fixing. I'll have to rip it back from the top to at least to the armholes, where it divides for back and front. Because I substituted a very different yarn to the one it was written for, I adjusted the row gauge, knitting 6 rows for every 4. I think I will be able to abandon this adjustment and just knit to pattern, and the length of the sleeves should turn out right. This will take care of the too-long body as well. The cowl shaping will happen over a shorter space, but I don't think that will be a problem.
I'm happy with the other modifications I made, one of which was essentially to knit the top part a size smaller than the bottom. This was very simple - the pattern has you increase from the waist upwards, to make a nice loose cowl top. I was afraid this would make the cowl too big for me. I love this kind of neckline, but many cowl/drape neck tops do droop way too low on me, and I really didn't want to wear a camisole underneath - 4 ply bamboo already makes a heavy summer top. I do have a B-string which is fantastic for certain necklines. But even that won't help with something really drapey - that's if I don't want to be restricted to standing up straight and never bending forward at all. I also didn't want to end up with an off-the-shoulder look. I worked out that the same amount of stitches would be about right for my hips and for my bust (this would still leave more ease at the bust than at the hips), so although it seemed weird, I left out all that increasing and just knit a straight tube until I got to the cowl shaping.
Another thing I changed was to just cast on a ribbed band, rather than making the garter stitch tie belt, which looks nice in the pattern pictures but which I was pretty sure would be sad and droopy and annoying in the bamboo. I love the way ribbing looks in this yarn.
The pattern is the Chiton Pullover, and the yarn is Cleckheaton Bamboo. The reknitting will happen... at some point.