Set margins or manual aspect ratio using desktop app

I am doing a series of videos for a client, and their aspect ratio (9:16) also requires I leave a margin of 10 pixels on all sides to accomodate their nav bars and branding. Other than eyeballing every frame of the video and trying to guess if my content is too close to the edges, is there a way to set a margin or manually set an aspect ratio to accomodate this?

This could be a major fail if I submit all these videos and content is cut off.

How can I make sure my content is within their template?

I am using the desktop version of Rush only.

Thank you!