Be careful what you cast on

I'm knitting a baby blanket for Kaliel, a very cool very young person of my acquaintance (my diplomat to Africa friend Brenda's daughter). I decided to make it out of cotton. I decided it would be simple stripes. I cast on some stitches. It didn't look like enough. I cast on some more. Still not enough. More cast on.

So, you all know enough about me to know the rest. The simple stripes theme interested me for three rows before I started experimenting with textural patterns which I keep changing. I decided that I would be doing vertical (long way) rather than horizontal (short way) stripes since it was obviously bigger than intended. I kept knitting. By the time it was big enough to really measure the length, it seems as if I cast on about 7 feet of stiches. Even at almost 2 feet wide it still has the proportions of a bright scarf. I'm scared about how long it will take me and I'm scared about someday casting off and finding out really how big this thing is. I'm haunted by visions of the fabulous 9+ foot scarf I made my friend Lisa (which I don't think she ever wore) from the caterpillar yarn.

I'll post photos someday, but in the meantime, I'm wondering if anybody has ever felted knitted cotton, or at least washed it on hot and shrunk it to be tighter. If so, did it work?