Cute pattern. I found this link to the pattern that links to tips for lining up and sewing 60 Degree Triangles. Maybe that will help??
https://sassafras-lane.com/products/arcadia-avenue
And here is the webpage they are linking too in the above link
https://sassafras-lane.com/blogs/new...g-60-triangles
One trick I do on my own is when piecing completed PP units together I line them up and look where they are lining up by moving the seam allowance out of the way so I am sure they are in the right place, then put a drop of EWSG (elmers washable school glue) and hitting it with an iron to set it, then sew.