The shortcode doesn't look the screenshots in the docs
Each theme will display the shortcode slightly differently.
Font sizes, buttons borders input sizes will all be affected by your current theme and perhaps also by other plugins.
If it doesn't look right to you, the first thing to check is that the WordPress visual editor has not added <pre> tags around the shortcode. Switch to text mode so you can see the HTML and delete any surrounding <pre></pre> tags.
Please do get in touch with if the shortcode still doesn't look good.