I square as I go. And when I assemble my top I sew the squares in 4 patches instead
of long rows. Then I sew the 4 patches in bigger 4 patches. Easier to keep everything
squared.
Have you checked your 1/4" seam allowance? Before I start a new project, I always test
my 1/4" seam. Different fabric and thread will make a difference. Here's how.
https://www.connectingthreads.com/tu...ance__D95.html
I also starch my fabric heavily before cutting. It helps stabilize the fabric
which makes it easier to cut and sew and there's no fraying. It's a must
for bias edges.