When my children were babies I made my own receiving blankets. They weren't any cheaper to make, but they were thicker, larger, and I liked them perfectly square....better for swaddling a newborn. Now I make them as gifts for new babies in the family.
I start by cutting a 40 - 42" square of heavy flannel.
Then I round the corners with whatever is handy...... a small dish usually has the right curve. Taking the time to curve the corners really helps later when doing the machine stitching....no tight corners to navigate!
I fold the blanket into quarters and cut all 4 corners at once with a rotary cutter so that they match. Then I stitch all the way around using a simple scallop stitch standard on many basic sewing machines.
Then I trim away the excess for a neat, no fray edge. On this particular receiving blanket I added a small heart of handwoven fabric so that it would match the heavier blanket it was meant to coordinate with.
Sorry, no finished photo of this. I gave the blanket away before getting a picture.