I cut the background fabric for the inner float border and sewed it on. then I cut the zigzag pattern fabric and tried it out for size and that brown strip just jumped out and looked wrong.
I thought about it for a while and carefully trimmed away the brown.
that left 31/2 inches and when I sewed it to the float border it didn't look balanced. It was too narrow and the float border was too wide. At that point I put it away. But it was there at the back of my mind and I wasn't getting anything else done. Sorting and packing were also on hold.
This morning I spread it out on my bed and auditioned the fabric I bought for the backing. Not bad, but I asked Jack's opinion. He didn't like either the zigzag stripe or the big dots. I was ready to take off the zigzag strip (it is only sewn on one side) and go borderless. I thought maybe a wider border of the background fabric would work. Well that was not good!
This is what I think I will do. I will add the rest of the zigzag strips and then another border of the background fabric the same width as the float border. I won't need to rip anything. I bought enough backing fabric so adding a a few more inches won't make a difference. I'm not sure yet about the binding but I will cross that bridge when I come to it.