The short rows are done and my slapdash math obviously worked okay. The first short row, I knitted to four stitches past the centre, turned and did a yarn over. (I’m doing Japanese short rows rather than Wrap and Turn.) The second row, I knitted 8 (back to the centre and four stitches past), turned again. Then each time I knitted back, I went four past my previous turn, including the stitch that I knitted together with the yarn over. I have now eaten up all the stitches and have widened the centre to about 4.5 inches, while the edges remain at two inches.
Now all I have to do is knit a couple more inches straight, bind off, and then figure out how to finish it off.
To join colours mid-row, all I did was knit both colours together for three stitches, which means I have tails hanging all over the place. I will have to decide which side I like best and weave the tails to the back.