Having slept a night on the problem of cutting the wrong side of the fabric and spending hours basting it to the lining I thought I might try something before ripping out the basting, sewing the dress wrong side out or just chucking everything in the dust bin.
Unpin the muslin pieces and reposition them the right way, see if there is enough seam allowance to harbour the pieces the right way down. Switch side pieces left and right with one another if necessary.
There is. Now I’m not paying attention to the carefully placed basting lines. I will have to sew the pieces together using the muslin edges and lines as guidelines. I am going to pin it crazy and then use a different coloured thread and carefully baste it by hand. After fitting I’ll sew it for real with the machine. Then remove all bastings.
At least I might be able to use this fabric. Sometimes it comes close though. The muslin is folded ON the seam line so that small piece of lining right there at the apex of the bust is all the seam allowance this piece is getting. Better stitch it sturdy.