Google analytics track multiple custom variables

I’m tring to use google analytics to monitor activities on my laravel site, as you can see i managed to record the events by $user_name witch is great however how to i associate this user name with another variable for example $project_id so i can see data for each user and on each different project.

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any idea how i can achieve this? here is my code:

<script>
$(document).ready(function(){
$(document).mousemove(function(){

  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', 'G-9YXX', {
  'custom_map': {'dimension<Index>': 'user_id'}
});

gtag('event', 'user_name', {'user_id': '{!!$user_name!!}'});

});

});

</script>