Aaah Be Careful ! On my first quilt I ran into trouble with half square triangles and it was suggested I try starch - so I did. But I used spray starch on unwashed fabric and proceeded to either shrink or distort the squares. Of course being so new I didn't notice until I had sewn the whole thing together and everything came out wonky. I ended up unpicking the entire quilt and recutting all the pieces a half inch smaller to make uniform sizes and then reassembling the now-smaller quilt. It all turned out okay in the end - but there was a lot of heart ache along the way.
By the way - the trouble I was having with half square triangles ? I have since figured out that if I had just pressed the seams before pressing open most of my troubles would have gone away. Ah experience - she is cruelly won sometimes.