Header image doesn't fill all of screen

Hi,
I’ve uploaded an image that suits the specified dimensions of the header. But the only option given is to crop the image which leaves a blank grey space to the right of the image. I can’t figure out a way of ensuring the whole image is uploaded to the header. This is only a problem on a large monitor, but even so I’d like to clean it up.

This is what I mean…. https://www.stephenfabes.com/speaking/

Any advice much appreciated

Cheers

Stephen