The Cue audio player provides an audio player widget with a dynamic playlist – delivering a fully responsive player for your posts, pages and widget areas.
The main site of the plugin is here. (I am not an affiliate seller.)
Download the free basic version of the plugin and you’ll likely find all you need.
The full version includes a cool audio player in the footer area of your website that keeps playing when people navigate away from your page (so long as they are still on your website).
Re the default audio player in WordPress…
To custom code the width of the inbuilt / default WordPress player use this code in your CSS (I suggest you use a CSS plugin such as this one to add CSS code).
The width can be pixels or a percentage (i.e.: 50%) of your page width.
width: 250px !important;
Have fun, and keep your WordPress questions coming in.