Hi there,
Currently, there are no such position to place your menu such as mega menu as it is designed that way unless you put them on your sidebar or on 'right' position.
Perhaps it would be best if you can submit a feature request regarding this issues by creating a new ticket on the forums and set it to "Feature Request" so that everyone else could vote for it. We will prioritize this feature during the development process for the next major version of office template if there are more people request on this.
Thanks for your understanding.