I looked on the Hobbs website, and their Heirloom washable wool shrinks 0-3%. Also, in their descriptions of their cotton battings, every one of their cotton battings shrinks 3-5%.
IMHO, 3% shrinkage is 1" per yard (36"), which works out to 1/4" for every 9", which is negligible. Also, if your quilt top is 36" before you quilt it, it will automatically shrink because of the stitching when you quilt it, so if it has to be 36" when you are finished quilting and binding it, you might want to consider making the last border a little wider, then trimming to 36" before you bind it. And did you prewash your fabric, because if you didn't, there may be a little shrinkage there.
I am one of those who doesn't pre-wash my fabrics, so I'm definitely not going to pre-wash my batting.