Dynamic width of horizontal bar across chart?

Hi, I’m new to utilizing plotly and I’m a Mendix developer. I’m incorporating a graph into my project and everything is working, however I need the horizontal bar at the top to dynamically fill the width of the graph and I’m not sure exactly how to do that.

Here’s the JSON data I’m passing to it. I’ve tried adding a fixed width under the ‘rect’ section just to try it out, but it’s seemingly not doing anything. Could anyone guide me? Thank you!