I feel your pain. We have all been there. I have a little bit of advice for you that MIGHT help.
-Stitch, press, measure, square up. Stitch, press, measure, square up.
I know that this sounds so basic and mundane, but it really does make a difference. I have found that if I measure my block after every seam and make sure that it is the size it should be, I have better end results. It takes longer---but it is worth the effort.
If your block consistently measures too small, then you can correct one of two ways---either make your 1/4" seams scant, or cut your fabric a little bit wider and then trim to size.
Some days the sewing machine gods just seem to be against us. I hope after you have had a chance to take a few deep breaths you will be able to go back in and make it all right.