gfg would be grandmother's flower garden, right? Octagons.
First of all, is it really necessary to square them up? I rarely need to square up blocks. However, if you really want to do it, my advice would be to draw the outline of a block (including outside seam allowance) on a piece of freezer paper, iron the freezer paper to your ironing board, then pin the block to match the outline, mist with spray starch, wait a minute to allow starch to be absorbed, then press carefully.