I also was afraid of "Y" seams and then I started working on a diamond log cabin pattern with mostly all "Y" seams. I'm thinking the instructions suggested to mark at every corner the 1/4" so you know where to start and stop. I remember taking a straight pin and sticking it into the little dot mark and then sticking it into the next piece I'd be sewing it to. Seemed to help as my quilt came out with very little problems. Also starching your fabrics helps a great deal as it will keep the bias from stretching too much as my diamond log cabins were mostly all bias edges.