Here's my favorite way to block knitting made from any fiber that can be washed:
Wash your towels. (!)
Take a spun-out damp bath towel and smooth it out on a flat surface. Place your sweater pieces on the towel one at a time, smoothing them out and rolling up the towel as you go.
Let it sit for several hours. Overnight is really good.
Un-roll your towel and lay out your pieces on a flat surface.
I use an inexpensive 3'x5' Indian-type rug. The fibers of the rug act like gentle Velcro and grip the sweater pieces, usually without pinning!
Gently ease your sweater pieces to the size that the pattern called for.
Let dry and you're all set to put it togeter!
This method works safely on any fiber content that can be dampened...