I was told by my quilting instructor not to pre wash. I did and it was kind of a mess with all the little strings etc, not to mention the bias moving around. So I was told orig to wash first, then she said don't do it, go figure.

Different instructors have different preferences.

If you overcast or serge the raw edges before washing, that eliminates/minimizes the raveling/fraying. I know it's an extra step when one is anxious to get to the fun part, but one will only "lose" about 1/8 inch of fabric on each end (under the stitching) versus up to 1/2 of an inch or more on each end due to raveling.