Double Curly Braces in quotes statement (custom RSS)?

I’m trying to change the default RSS format to make my Hugo site into a podcast host. I created a shortcode for audio in posts that turns…

{{ audio CTJ 001 }}

into an audio tag pointing to

I’d like to do the same for the RSS feed. I’m getting an error. I’ve attached screens of my RSS formatting, an example post providing the params, and the error I get when I try to access the XML file on my local.

Please advise – thank you!

Screenshot from 2017-08-23 13-59-08

Prepended “.Params” to my… params.