You have to plan and lay out the 1/2 hexagons. Every other half is rotated upside down. That is how you avoid the Y seams.
You either sew a 1/4 hex at the beginning or end of each row, or you can just trim the sides when you are done sewing them all together.
The class that cutebuns taught on OBW's shows this method. You may not be making the same type of block, but the theory is the same :wink: :D:D:D
Search for the portion of the class that is teaching sewing the blocks together, I think the class had 4 parts to it.