Use the attribute “excerpt_length” to control how many characters in your excerpt you want displayed.
[wc_posts author="" author_name="" p="" post__in="" order="DESC" orderby="date" post_status="publish" post_type="post" posts_per_page="10" taxonomy="" field="slug" terms="" title="yes" meta_all="yes" meta_author="yes" meta_date="yes" meta_comments="yes" thumbnail="yes" content="yes" paging="yes" size="large" filtering="yes" columns="3" gutter_space="20" heading_type="h2" layout="masonry" template="box" excerpt_length="30"][/wc_posts]