Two good questions have come up: one – how do you handle the seams that are underneath and flip the wrong way when sewn? The first thing I would do is pin them down before sewing to prevent the “flip”. Our second photo shows only one pin but using another on the left side of the stitching (closer to the thumb in the photo) would help a lot. However, since occasionally, no matter what, “flips happen” – instead of ripping out the flipped area of the seam, you can try snipping the seam allowance just below the flip and pressing the rest of the seam again in the correct direction.
The other question was regarding nesting seams for lattices. I’m guessing this means when a sashing has cornerstones or “posts” at every corner. The same principle works here, press seams that should match in alternating directions before sewing. However, if you don’t have cornerstones and you mean that your lattice isn’t straight on the quilt top – measure all your blocks before adding sashing. Trim them all to the same average size, Then add your sashing. Also, double check that your seams are a true 1/4″, not even a hair bigger. That will make the sashing/lattice straighter and the blocks truer to size.