This morning I put it in the machine once again to wet it thoroughly.
Over at Pauline's house we laid a couple of sheets on the carpet and spread out the quilt. It's quite 'flexible' whilst wet. When it looked right, I measured the diagonals, they were just one inch off. So so little adjustment to get the diagonals even, all that's needed is a little lifting with a slight pull and then lowering again. I didn't pin it at the edges as it didn't need any strong stretching in any direction to make it square. I've left it in her closed room with a couple of fans on it to collect it on Monday when it should be dry.
If you click on it you should be able to see the quilting.