my go to technique for washing smaller pieces is to serge the edges and throw in the washing machine and dryer...yep...I know I will lose some fabric but mot likely to be much more than what I would lose anyway by straightening the edges. I get a bit leary of gentle means of prewashing, cuz, I'm not sure if that method would shrink or test the colorfastness of a regular washing machine. I usually toss in a few of those color sheets in the wash too. If there is a lot of color on them, I will rewash and not use the fabric if warranted.