in my case 'Align' helped :

 @override
  Widget build(BuildContext context) {
    return Align(
      alignment: Alignment.topCenter,
      child: SingleChildScrollView(
          child: const Column(
            children: [
              Text('Search box'),
            ],
          ),
        );
      }

taken from this post:

https://www.reddit.com/r/flutterhelp/comments/1abq8av/singlechildscrollview_centers_content_but_need_it/