It took a while to work out how to tackle this one, but eventually after many scribbles I got the courage to take a pair of scissors to the fabric:
Then I thought I'd be really clever stitching on the last black stripe to hide any bits where things didnt line up properly. Great plan, until, while ironing inside out, I saw what I thought were leftover basting stitches and UNPICKED them. I was infact unpicking my delicate hand stitching, and didnt realise until I put my dress on before the party. OOPS.