For some reason I have never been a cornerstone fan, so when I lay down a row to pin for sewing, I visually see how each row is doing by looking "backwards". Don't just pin end to end and expect the current block to align with the previous block. Check to see how they look while they are laying right side to right side, before you pin/sew. Make adjustments as necessary. You can take a lot of that wonkiness out by fiddling with the row and visually seeing where the block should be moved to come into alignment.