How to configure X server to fill the screen over VNC/noVNC?

I am running an Xfce desktop environment in Docker from [here](https://github.com/ConSol/docker-headless-vnc-container) and connected to it using a VNC client and a browser (backed by noVNC) but in both cases the output doesn't fill the screen - or at least the dimensions of the output don't change so that when the output hits the edge of my local screen there are gaps. Is there a way I can get the output to fill my local screen by dynamically adjusting the dimensions/resolution? Or would I need to work out my local dimensions manually first and reload X/VNC? (quite new to how GUIs work in Linux work so not too sure if this is something that'd be configured in VNC server or in X server)