That layout in particular is difficult to modify because it has a lot of custom javascript.
After seeing your design, I think this template is a better starting point "Dynamic Remarketing with Headline and Individual CTA Buttons" and is easier to modify, but if you don't feel like starting over you could zip your entire project folder, upload to Google Drive, share a link, and I will take a look. (The file sent already was the published file, but I need the GWD author file).
Hope that helps,
Kent
Google Web Designer team