Don't enlarge a block.
Look at the block size and figure out how many more will be needed to get to King-sized.
It may only be needed for width, quilt lengths are usually around 80" so if it's that or more on your pattern you'll just add blocks for width.
The other thing not to do is add additional borders - will ruin the design. Rest assured, had the designer wanted more borders, she'd have included them.