Diana---Your airplane quilt turned out really cute.
I understand your frustration-I think lots of us have had this same problem at one time or another.
I would like to add two more hints that you may or may not find helpful, but I am going to throw them out there anyway. When your blocks are applique, cut your background fabric an inch and a half bigger than your finished size to start with, do the applique and then trim and square up your block. Applique can tend to stretch or misshape the background fabric and this will help you to have consistent size blocks. (for a 12" finished block, you would want to cut background fabric 13 1/2" to start with and then square up to 12 1/2" when you are ready to assemble)
The second tip is for your sashing strips--if I have enough fabric I cut mine 1/2" wider than called for, sew on one side, press, and then trim to finished size + 1/4" (the seam allowance for the other side). This keeps me from having "off" seams on both sides of the sashing and tends to make them a little more consistent width. It is really helpful for narrower sashes and borders where even an 1/8" can be glaring. Hope this helps.