Thank you for the advice and so quickly too!
I will try stitching just to the side of the drawn line to allow for turn room. If I am still struggling I will try the oversize squares and then cut to size although I am quiet determined to get it right using the right sizes in the first place (even if it means having to pull more hair out!). Also I will press before I cut to make sure I'm squared.
Re Aurifil thread, this is what I am using, the 50 wt, I love the stuff! I've also got a nice thin needle (Microtex 70).
I can't wait to get cutting more blocks now. I am going to cut some practice pieces first though until I get it right instead of being so impatient and rushing right into working on the actual blocks.