How to resize render texture to screen resolution?

There is another post here that uses a shader to render to the player camera, but that doesn’t seem to have what I am looking for. I currently have a camera that renders to a render texture, and every frame that camera is updated to the local player’s head position. This camera has culling set up so that it will only draw the player’s mirror reflection. Eventually I want to do some math to move the camera around as if this is a fully 3d reflection, but at the moment there is an issue where the view is stretched if the game’s aspect ratio is not the same as the camera.
I’m not sure if I should be changing the aspect ratio of the render texture or the aspect ratio of the camera, and how to do that. Overall I’m very new to udon.
I’m coming here for help, and any help is greatly appreciated.

Thanks.

EDIT: here’s a demo of what I’m talking about

I’ve worked out the quaternion math and some simple positional stuff and I have a product I’m happy with. demo here Only problem is for the result to be convincing the aspect ratio needs to be perfectly square… I still don’t know how to answer my first question, but hopefully this video demonstrates more of what I’m saying.