Starch is really not necessary. I've quilted since the 70s and never use it. The point is to be accurate in every step. First, make sure the pattern is accurate. Hello, sometimes they aren't! Trace and/or cut accurately. Piece with an accurate ¼-inch seam allowance. And when you press--don't push the iron back and forth. All your careful work will be distorted. Pressing is a gently up and down action. When you're done with this your blocks should be the measurement intended. Good luck, quilting is a wonderful occupation and so creative.
SandyQuilter