An unexpected halt to progress

I've been motoring through the join-as-you-go part of my sofa bed afghan. At first, I did really well with weaving in the ends as I went, and the whole first panel was completed and neatly sewn in all in one evening.

Forgive the mess and the bad light, it was quite late

The seam you get with joining as you go is very neat. Rather than sewing the entire edge of the squares together, you just crochet the spaces between the dc clusters. The only really tricky part is making sure the corners of each square still look like corners!

Here's a close up of the joining. All of the black edges to these four squares have been added when joining. You can't tell the difference!

Here, I'm joining a big square to a little square. The little square (on the left) has already had it's black final round added; as I crochet the final round onto the big square (on the right), I'm replacing my chain space with a slip stitch into the chain space of the square it's joining. So simple!

This is as far as I've got, laid out on the bed it will live on to give an idea of how it will look when finished. I'm sure the eagle eyed among you will have noticed that my nightmare has come true.. I've run out of yarn! I still have the rest of this panel, and the fifth and final panel to go, plus the border.

The trouble is, this yarn only comes in 400g balls, so I am going to have loads left over. I'm hoping they have it in Hobbycraft as I will be popping in there tomorrow to buy wedding related things; otherwise I'm going to have to justify more yarn purchases as when I order from Deramores, it always seems silly to pay for postage when you could just get more yarn and have free postage. I do need more Marble Chunky for my replacement Crochet Lacy Wrap....