Today we'll put in the zipper and finish the back seam! Your dress is almost finished. As I mentioned in the end of yesterday's post, I went ahead and sewed the side seams before doing the back seam (step 28 in the pattern). I recommend you do the same. If you need to take your dress in or out bit, it sometimes works better to do so from the back than from the sides because the armholes won't grow or shrink in the process. That being said, for dart placement, etc. it can be better to take things in at the sides. Once you finish the back, you could still subsequently alter the sides. With this dress, I thought it would be difficult to alter at the sides because the gathered pieces are all at the sides, which makes it difficult to pin everything in place while wearing it (even thought there isn't any gathering at the side seam itself).
Try on your dress. This step should be in the pattern instructions, it's so important. Pin the back shut (it's easier to do this if you have help). Mark where the back seam/zipper should go to make the dress fit perfectly. For me, this meant a 1" seam at the top of the back (waist and above), and a less than normal 3/8" seam from my hips down. This corresponds to taking the dress in 3/4" up top and taking it out 1/4" on the bottom. Unfortunately, I got lazy and really only paid attention to the top 1" seam, so I took the dress in all the way to the bottom, resulting in a dress that fit way too tightly on my butt and legs. Once the zipper is in, you won't want to take it out to make changes! I ended up making my changes along the sides.
Unpin your dress and even out your markings. You can trim everything to a 5/8" seam if you're taking the dress in, or just remember to sew along the markings you made without worrying about the excess fabric.
Push the lining out of the way. If you stitched the back neckline all the way to the edge of the fabric, undo about 5/8" (or up to your markings) so the top of the zipper can line up with the top of the fabric.
Steps 22-26 describe now to insert an invisible zipper. Some of these steps violate rules I learned are important, such as never closing the zipper after you press it flat until after you've sewn the whole thing in place. I recommend you follow my zipper how to, described here (and including video).
So put in your invisible zipper, finish the back neckline seam (sandwiching the top of the zipper into the seam), and understitch the back neckline seam (the pattern recommended doing this in step 16, but I told you to save this understitching for later). Now is the time!
Finally, stitch your back seam below the zipper to the large circle near the bottom. This is the top of the vent. You will end up with a small gap between the bottom of your zipper and the start of this seam. You'll close that up by hand later (or now if you're feeling eager). I didn't take any pictures of this step, but it should be self-explanatory.
27. Stitch center back seam of back lining between circles. The top circle is the bottom of the zipper. The bottom circle is the top of the back vent.
Unfortunately I don't have a picture at this point, but it should be self-explanatory.