If you sew right on the line, the corners might not line up - if you sew just a tiny bit outside the drawn line, that will account for the width that the thread takes up inside the seam.
When you fold and trim, you'll get a better square.
I serged this quilt, but sewing is the same - you just have to trim off the extra triangles afterward. :)
Have fun!
Snowball quilt - lay four smaller squares at corners of the large square. Draw a diagonal line across each of the smaller squares. (highlighted pink)
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Sew on the line or just barely outside the marked line - the perspective is off in this picture, so ignore the needle and just look where the pink line is compared to the line drawn on the fabric. :)
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