For a prezi with a url of https://prezi.com/view/taTbCHVyuHxsYyu5ThNy/

you need to use this shortcode

[prezi url="https://prezi.com/view/taTbCHVyuHxsYyu5ThNy/embed" height="560" width="996" zoom_freely="N" ]

Which will look like this:

NB the height valuse is used for both height and & width.