Becky, I suggest you lay your quilt top over your batting, cut off some of the excess (what you won't be needing) and measure out (cut) an exact square of it, then wash that small square. Maybe like 12" square. Just be sure to measure it. Soak it good in cool water, put it into a very low temp dryer, or whatever temp you will be drying your quilt in the future, and see how it does, by measuring it again. (Sometimes a batting will shrink more one way than the other.) I hope to never have to wash my art quilt with the wool batting, but with cold water, a good squish between towels, and a tumble air dry, I have faith mine will not shrink a bit.
Dawn.