Exporting to WebM from AE Problem

I'm trying to export a simple animation from After Effects to a WebM file so it can be used as an OBS alert for my Twitch stream.

However, when I export and render through AEM, the colour washes out and for some reason it has shifted my animation off centre and to the right by 50px. Not sure why it has done this. This is what the colours should look like below:

This is what the WebM looks like:

This is what the WebM looks like in comparison to the originaal baackground colour:

And here are my render settings:

I would appreciate all the help as I have very little experience with the technical side of After Effects.

Many thanks!