Ok I know you're all wondering what happened to the dress. I wanted an invisible zip put in the 'proper' way which meant not only the bodice had to be lined - it was - but the skirt part also needed a lining skirt. I didn't realise this till I'd attached the bodice lining. So after a bit of worry and a bit of unpicking. I went and cut a skirt from the lining fabric and sewed it in then finished the zip part.
Lastly I attached the frill on the bottom of the dress and there you have it!!
If I had gone about it the right way from the start it would not have been a drama, but I didn't think about the zip needing that facing all the way to the bottom. Please note the near perfect invisible zip!! I am pretty proud of that achievement. It's so hard to get the second side of the zip in the exact position as the first side. I learned a little trick and that is to put in a few holding stitches in the position you want, before you sew it in.
And here's the dress before the skirt lining was put in, you can see what I mean.
I understand now how it works, but I'm not sure I could do another without help. Sewing is not easy all the time.