The points will come to the end of the triangle and that's OK until you do the assembly of the final block. When you sew up the seams to make each row you take a little bit of fabric away and you get the 1/4 inch margin you need. This took me *ages* to get my head around.
I kept thinking the BOM instructions were 'wrong' but I could see everyone else was doing it 'right' from the BOM pictures people were posting. Then I finally worked it out.
If you want I'd be happy to do a block 'together' with photos across the ocean (assuming you're in the US.) PM me if you're interested. Only problem is my sewing machine is currently in for a service and I won't get it back for another week or so. Until then all I can do is cut fabric and post messages on this board. Keep trying, you'll get there :-)