There are several choices to be made in assembling the two panels of the baby blanket. Here are two of them: which selvedges to butt together (I'd like the stripes to have bilateral symmetry).
I chose the second arrangement. First I butted the two panels together and joined them invisibly on the sewing machine. Then I chose one of the warp yarns and handstitched a decorative join over the machine stitching.
I've used this triple zigzag seam many times, and I know I've seen it described in several ethnic embroidery books, but after an hour searching through my badly organized library, I'm unable to unearth a single reference. If you recognize it, I'd appreciate hearing from you. Meanwhile, here's my own crude stitch diagram. The blue line represents the seam where the two panels come together. The red line is the stitching.
The needle comes up at A, goes down through the crack and up at B, down through the crack and up at A, down through the crack and up at B, down through the crack and up at C, down through the crack and up at B, down through the crack and up at C, down through the crack and up at D, down through the crack and up at C, down through the crack and up at D, down through the crack and up at E, down through the crack and up at D, down through the crack and up at E, and so on.
That's a lot of words, but after a few passes it becomes automatic. The seam looks the same on both sides, and is a nice adjunct to handwoven fabric.