Here's my suggestion, Do the pinning as Rachel suggested only machine baste across the seams to see if everything matches before the final sewing. The basting can be left in then you don't stretch anything out of whack by removing the basting. I would also suggest sewing a scant 1/4 inch, this is one thread less than the full quarter which allows for the width of your thread.
(Check your stitching on some scraps, and see if you need to do some adjusting.)
I also check my seams frequently to make sure I am at the 1/4 inch mark. On some blocks you can get by with a little over or under if they are a consistent size but not when matching points.
You're getting lots of good advice, but sometimes it's only patience and practice that works.
Longarm