No, I'm not a pre-washer. When I took my first class at my LQS they advised us NOT to, and so I have gotten in the habit of not, and up until now it's never been a problem.
I did once, before that first class, wash all my fabric (in preparation FOR the class)and it was a disaster!!! It all frayed HORRIBLY and also I had SO much waste when squaring it up to get ready to cut! So since then, since I've had good results from not pre-washing, I've stuck with that.
I did just go and spray a piece of the fabric with water and it did shrink. I'll just have to start making sure I starch before I cut.
Oh, and it's most definitely 100% cotton. The shrinking actually happened right in front of my eyes AS I sprayed it, but from what I read above, the heat must have shrunk it more. ugh.