Changing slider width & height issues

Hello. I have followed everything written in the description, however I am having trouble making the slider smaller. I added the “set_flexslider_hg_rotators” function and “add_image_size” functions to the bottom of the theme’s functions.php file, but specifying the image size for the homepage-rotator does not work. I am using the following shortcode:

[flexslider slug=homepage]
Here is the code I have added to the bottom of my theme’s function.php file:

function set_flexslider_hg_rotators( $rotators = array() )
{
    $rotators['homepage']         = array( 'size' => 'homepage-rotator', 'heading_tag' => 'h1', 'options' => "{slideshowSpeed: 7000, direction: 'vertical'}" );
    $rotators['contactus']        = array( 'size' => 'thumbnail', 'orderby' => 'title', 'order' => 'DESC' );
    $rotators['gallerypage']  = array( 'size' => 'medium', 'hide_slide_data' => true );
    $rotators['amenities']        = array( 'size' => 'your-custom-size' );
    return $rotators;
}
add_filter('flexslider_hg_rotators', 'set_flexslider_hg_rotators');
add_image_size( 'homepage-rotator', '300', '150', true );

Is there something I have done wrong?

https://www.ads-software.com/extend/plugins/flexslider-hg/