Echo the return value from wp_get_attachment_image_src(). It also returns an Array(), so you need to grab the needed part from that array. In this case it’s the first/0 value. Example:
<?php $bgImage = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'full' ); ?>
Include tha variable inside the inline stylesheet
<section class="contact-cover" style=" background: url('<?php echo $bgImage[0]; ?>'); background-size: cover; background-attachment: fixed; padding: 60px 0;"> </section>