It could shrink with agitation during washing. If a friend handmade it, I would have it dry cleaned to avoid damaging it.
If that's not feasible, fill a sink or pan with cold water, add just a few drops of detergent and lay the blanket in there gently. Let it soak a bit. Work the water through the fibers by VERY gently and carefully squeezing the fabric one section at a time, being careful not to agitate the fabric too much. Drain the water out and then rinse it with cold water -- again, no agitation. Squeeze excess water out in same way. Carefully lift blanket out of pan/sink and lay flat to dry on towels. You can remove more moisture by rolling in towels and squeezing. When you're ready to let it dry flat on towels, maneuver the blanket into the proper shape, as it will dry into whatever shape it's in at that point.
I've hand washed wool sweaters this way, as well as hand knit pieces, in order to block