First, open a desired template in new window and click on copy button (click anywhere inside a block and then from section settings click on copy button icon) 2. Go back to your website editor and click on blue colored icon to add a section. 3. click on the paste button at the available at the lower left corner.
Through this way you can copy any template without formatting your complete website and content.
If this method does not work, try changing your browser or clearing cookies/cache.