Let me backtrack for a moment to thank all of you who stopped by my blog or posted on PatternReview to make suggestions or offer sympathy. Your thoughts are much appreciated.
Now back to the blouse. As I mentioned, I started again, this time without the underlining. I now know for certain that the puckering is caused by the linen/rayon fabric shrinking when I press it. Even on low heat, without steam. However, with careful pressing, I've definitely minimized the problem. You can see there's quite an improvement. I think it will be okay once the finished blouse is washed. There's sure to be some general shrinkage and I'm hoping the puckers will disappear into that. And that the blouse will still fit.
Here's the back side of the seam. I just overcast the the seam allowance, then trimmed it down after top stitching. I'm reasonably satisfied with how it looks. I actually would have preferred the finish to end up narrower because of the show through, but I didn't want to serge the seam allowance because I didn't want the added bulk and because I wanted the double topstitching.
So that's where I'm at right now. I'm kind of excited because today, I'll actually get to sew a different seam!
* I apologize for the quality of the pictures. I never realized before how difficult it is to photograph white!