Acrylic yarn is made of plastic extruded from a machine. Unblocked knitted cloth curls at the edges and may look fuzzy. The conventional myth is that trying to block acrylic yarn will melt the yarn or that the blocking will not hold. While this is true if you apply heat directly to the fabric, there is a way to block acrylic yarn using steam that will uncurl the edges and make the pattern stand out.
Measure the knitted fabric with the ruler to check whether the knitting is the size called for by the pattern.
Pin the knitted fabric to the blocking board by inserting t-pins at the edges of the fabric. If the fabric is not the size called for by the pattern, then stretch the fabric while pinning it to the blocking board.
Set the steam iron to the lowest steam setting.
Steam the fabric by running the iron an inch above the fabric. Be patient; do not press the iron to the fabric, as it will melt the yarn. Stop when the fabric is slightly wet.
Allow the fabric to dry while pinned down.
Pressing the iron to the acrylic yarn will change the fabric by melting the yarn. Some people like this effect, but it may destroy the look of the knitted fabric.