I agree... the only "scant" should be your seam. To set the size of your seam, a 3x5 card *should* have 1/4 inch line spacing. I use this to be sure where the edge of my fabric should be and where my needle should be set. To determine your cutting and sewing, cut 3 pieces (short is ok.... 6 inches or so) of fabric 2 1/2 inches wide, sew all three together side by side, the middle section needs to be exactly 2 inches. If it is, everything else you sew should be perfect.
There was a quilt teacher a long time ago (wish I could remember who is was) who talked about *your* personal perfect measurement. Her theory was that as long as you cut and sewed everything the same, your points would match. I have found this to be true, however, if you were doing a project where your block (perhaps you are swapping with friends) needs to be a specific finished size, this won't work!