Are you trying to redirect to the post that was just created?
From the acf_form() documentation
http://www.advancedcustomfields.com/resources/acf_form/
/* (string) The URL to be redirected to after the form is submit. Defaults to the current URL with a GET parameter '?updated=true'.
A special placeholder '%post_url%' will be converted to post's permalink (handy if creating a new post) */
'return' => '',