How do I center form to the middle of the screen? – Flutter

I’ve tried using mainAxisalignment, and even wrapped it into a Align property and a sized box property but nothing seems to be working. I am trying to align both the form and the button presented into the middle of the screen. I’d like to know how I can solve this and why it wasn’t moving or working before.

Code:

import 'package:flutter/material.dart';
import 'package:qr_flutter/qr_flutter.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(),
      home: Scaffold(body: MyCustomForm()),
      debugShowCheckedModeBanner: false,
    );
  }
}

class MyCustomForm extends StatefulWidget {
  const MyCustomForm({super.key});

  @override
  MyCustomFormState createState() {
    return MyCustomFormState();
  }
}

// Create a corresponding State class.
// This class holds data related to the form.
class MyCustomFormState extends State<MyCustomForm> {
  // Create a global key that uniquely identifies the Form widget
  // and allows validation of the form.
  //
  // Note: This is a GlobalKey<FormState>,
  // not a GlobalKey<MyCustomFormState>.
  final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return SizedBox(
        child: Align(
            alignment: Alignment.bottomCenter,
            child: Form(
              key: _formKey,
              child: Column(
                children: [
                  TextFormField(
                    // The validator receives the text that the user has entered.
                    validator: (value) {
                      if (value == null || value.isEmpty) {
                        return 'Please enter some text';
                      }
                      return null;
                    },
                  ),
                  ElevatedButton(
                    onPressed: () {
                      // Validate returns true if the form is valid, or false otherwise.
                      if (_formKey.currentState!.validate()) {
                        // If the form is valid, display a snackbar. In the real world,
                        // you'd often call a server or save the information in a database.
                        ScaffoldMessenger.of(context).showSnackBar(
                          const SnackBar(content: Text('Processing Data')),
                        );
                      }
                    },
                    child: const Text('Submit'),
                  ),
                ],
              ),
            )));
  }
}