In my experience, blocking doesn't really work with acrylic yarn. If you try to use steam on acrylic it will "kill" the knitted/crocheted piece unless applied really, really lightly - just hovering above the piece with the steam .... and, even then, it doesn't block as well as a 100% wool piece will.
The other alternative is to pin your squares out on a foam board, spray them lightly with water, cover with a clean cloth and leave overnight to dry. This will "fix" the acrylic item into shape, but only lightly.
I, personally, use the very light steam method above the worked piece, but you have to be very careful not to over-steam it. I just pin it into the shape required, apply a very light steam, and then leave to dry completely before unpinning.