I learned from watching Lessa Siegele's episode on The Quilt Show to make units a bit oversized and then trim them down (yes, trim each unit - it really doesn't take a huge amount of time when you do it as an assembly line). Trying to cut precise patches and sew precise seams has NEVER worked for me in 25 years of quilting. Lessa's technique works!
For those interested, it's episode 1801 on The Quilt Show. (It's a monthly subscription but has been worth every penny to me)
https://thequiltshow.com/watch/2016-...-lessa-siegele