Please help!

In an attempt to de-yellow the lace on a Cherry Ribbon Sundress I'd just bought second hand, I used a strong stain remover containing bleach and rubbed it into the collar. I thought I had protected the fabric underneath with paper towels, but the stain remove leaked through and now the colour has run!

Does anyone know how to save the dress before it's completely destroyed? Will washing it in cold water help?

Please help, this is my dream dress D: