:oops: :oops: I've figured out what I was doing wrong.
I was trimming the seam allowance BEFORE I pressed the corners back.
I tried a square by flipping my corner back on itself to create the little triangle corner (making sure the corner was square),then I pressed it, then gently folded it back out , THEN I trimmed.
Came out a perfect 3.5"! :shock:
Since then, I've completed 10 perfect little squares. :D
Sometimes I scare myself by not thinking (or thinking too hard!) :roll:
Oh well, guess I learned something after all.
Thanks for the help!