And it turned out OK! I french seamed all of the inside and it looks beautiful! I think I still need to cut a slice out of the neckline of the dress as it has some excess fabric there which can look strange. I thought I might have to lower the neckline very slightly but in actually wearing this I realised that I didn't need to, it didn't catch my neck at all.
After I made the peplum I realised that I hadn't allowed enough space in the rear so added these little panels to either side of the centre back seam to make it wearable - I had my first major sewing error in the cutting of these panels when I cut into my already sewn right back peplum piece by accident! Thankfully I had enough material to cut a new piece and the extra panels, but it was pretty gutting!