fix small align issue in example app

@@ -23,8 +23,9 @@ class MyHome extends StatelessWidget {
   Widget build(BuildContext context) {
     return Scaffold(
       appBar: AppBar(title: const Text('Mobile Scanner Example')),
-      body: Column(
-        mainAxisAlignment: MainAxisAlignment.center,
+      body: Center(
+        child: Column(
+          mainAxisAlignment: MainAxisAlignment.spaceAround,
           children: [
             ElevatedButton(
               onPressed: () {
@@ -100,6 +101,7 @@ class MyHome extends StatelessWidget {
             ),
           ],
         ),
+      ),
     );
   }
 }