I have calmed down a lot, though, and I think that what I will do is:
1) Finish the centre pannel and work the mitred increase rounds--I have more than enough yarn for that.
2) Buy another ball (screw the dye lot) to work the edging. By my calculations I should be able to squeak the edging out of 1 skein.
Here's a picture of the pattern:
In answer to the questions, no stupid me I did not put the dye lot on Ravelry, as I bought the yarn and started the project before I joined Ravelry and by the time I added the details to Ravelry the ball band was already missing. Plus even if I knew the dyle lot it's been a while since I bought the yarn so I don't know how easy it would be to get more of that lot.
I knew I was in trouble because when I joined Ravelry and took a look at other people who had knit the same shawl in this yarn, most of them used more yarn than the pattern called for.