If you remember the name of the yarn, you could try looking it up on YARNDEX
to see if its machine washable...if it has ANY acrylic content, it shouldnt felt in the wash, I THINK.....( I should add SOME kind of disclaimer to that statement,just in case)
Had you done a gauge swatch? (Not like I ever do gauge swatches...) With chemo caps that may be more important since you want it to be snug.
You may want to try doin it on smaller needles.....