Making a c2c blanket with stripes in prime numbers of rows

Planned size 100x140 cm or 55x66 blocks
Using 4 mm hook and c2c stitch with double crochet,
Chain 6 plus 3 dc for increases
One block is approximately 1,8 cm

Rows are in alternating primary colors and white

When 66 rows height, start decreasing on other side too

Planned next rows see stitch fiddle chart
Had to adjust pattern because I ran out of red yarn