Do you think you have "elbows" from when you cut the strips? I had a bit of bother too and had to delete the offending strips....

When sewing the strips, you sew the first two strips together, then from the OTHER END you sew on the next strip, THEN REVERSE TO THE OPPOSITE END for the next one.. etc. etc. with each row you sew....

When sewing strips lay the materials flat on each other and don't stretch the top or bottom materials...

You will have it sorted out by now as this was started over a year ago.... hope it all went well....