as you use multiple $testimonials i suppose those are group values.
then you need to use get_sub_field() in place of get_field()
so it should look like
$term = get_queried_object();
$testimonials = get_sub_field('testimonials',$term);
echo $testimonials['small_title'];
echo $testimonials['main_title'];
echo $testimonials['description'];
Please refer to ACF documentation when you use non classical fields.
https://www.advancedcustomfields.com/resources/group/