I agree it doesn't look too awfully un-square in the photo. If you decide you can't live with it the way it is and are willing to undo the rows down to each block, then I may have a solution for you. I recently discovered this square-up method when teaching my 11 year old daughter how to quilt blocks with a wide variety of techniqes over the last 5 months; we ended up with a few wonky blocks that were upto a quater inch off square. Here's what I did to fix it...
Trace onto a piece of freezer paper and cut out a square the intended size of the block. Layer the block, centered on top of the waxed side of the freezer papper, and start secureing it to your ironing board surface with pins. Pin around the outside edges, working from side to side, easing the fabric edges as you go to touch or overlap the permiter of the freezer paper. Once you've gotten it as close as possable, saturate the block with spray starch or Best Press spray. Readjust the pins if necessary to get it to lay flat, and aligned or overlapped with the freezer paper edge, then press with an iron until the fabric is somewhat dry. Remove the pins, turn the block upside-down, and iron again to secure the freezer paper to the fabric. Now with rotary cutter/mat/ruler, trim any excess fabic that overlaps the freezer paper edge; and carefully remove the freezer paper. The block should now stay square long enough to be able to achieve straightly sewn rows. A single freezer paper square can then be reused in this manner for upto 4 or 5 blocks. If your block has points that need to interesect with points in other blocks, be careful not to trim away all of the seem allowance.