Hi there,
The place of the widget addition is not suitable for the purpose you have judging the sample link you gave us. I suggest that you add a Child Theme and in the functions.php file of the Child Theme at the end add this code:
add_action('x_after_the_content_end', 'add_to_footer', 1);
function add_to_footer() {
echo do_shortcode('[alert type="warning" close="true" heading="Warning"] This warning box has the optional close button turned on. Try it out. [/alert]');
}
The code above uses the ** x_after_the_content_end** action to add whatever code is outputted in ** add_to_footer** function at the very end of the page before the grey footer section starts.
Now inside the function, I used the do_shortcode WordPress function to be able to add whatever shortcode I like there.
For the demonstration purposes, I added a simple Alert shortcode. You can add whatever shortcode you used for the Instagram feed there.
For more information about the customization of the theme I suggest that you read the articles below:
https://theme.co/apex/forum/t/customizations-actions-and-filters-in-x/208
Needless to say that the customization requests are outside of our support scope and the code hints above is an attempt to get you started on the further customizations.
Hope it helps.