Consider having a template made out of plexiglass or similar item. A hardware store, like Lowe's, or a an independent store can trace around the block pattern and cut it out for you.

The quilt is beautiful. I love how it makes me think of underwater relaxing.

We made one very similar in our quilting group using a flexible thing to make the curve. Many liked it. I did not enjoy making it and did not enjoy the result, gave it to charity.