Center items as long as there are only few items on the list which does not exceed available screen size and when it does and scrolling is available left align all items in the list view.

horizontal_list_alignment.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  List listItems = ["A","B","C","D","E","F","B","C","D","E","F"];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        width: MediaQuery.of(context).size.width,
        color: Colors.lime,
        child: Container(
                color: Colors.lime,
                child: Center(
                  child: ListView(
                    shrinkWrap: true,
                    scrollDirection: Axis.horizontal,
                    children: listItems.map<Widget>((a) => CircleAvatar(
                      child: Text(a))).toList(),
                  ),
                ),
              ),
      ),
    );
  }
}