Quilt in progress - layout

After a morning of dither and deliberation about the colour and type of background, in the afternoon I chose a black bit of sateen that had once been a large pillowcase and started to lay out the blocks, only to find that they wanted to snuggle up to each other, hiding the background -

About 90cm high. Colour is yellowish because of lighting conditions

Having laid them down, I need to take them up again to tidy and trim a few edges, and then fix them to something quite solid so that the edges don't droop. The centres of the blocks are nice a firm but the edges are often floppy. Hah, while writing this, I glimpsed a way forward - reinforce the blocks on the edges but not those in the middle...