Disables form submission when pressing Enter, unless user has tabbed to submit button or page advance button.

gf-enter-prevent-submission.php

<?php
function twxyz_prevent_gform_submission( $form ) { ?>

  <script type="text/javascript">
    jQuery(document).bind('gform_post_render', function(){
      jQuery(document).on( 'keypress', '.gform_wrapper', function (e) {
        var code = e.keyCode || e.which;
        if ( code == 13 && ! jQuery( e.target ).is( 'textarea,input[type="submit"],input[type="button"]' ) ) {
        e.preventDefault();
        return false;
        }
      });
   });
  </script>

  <?php return $form;

}

add_action( 'gform_pre_render', 'twxyz_prevent_gform_submission' );