There is a Very Simple way just use centered_grid package :-

1. install By typing flutter pub add centered_grid and copy paste this example

   import 'package:flutter/material.dart';
   import 'package:centered_grid/centered_grid.dart';
   
   class ExamplePage extends StatelessWidget {
     final List<String> imageUrls = [
       "https://dummyimage.com/180x150&text=1",
       "https://dummyimage.com/180x150&text=2",
       "https://dummyimage.com/180x150&text=3",
       "https://dummyimage.com/180x150&text=4",
       "https://dummyimage.com/180x150&text=5",
     ];
   
     @override
     Widget build(BuildContext context) {
       return Scaffold(
         appBar: AppBar(title: Text("CustomGrid Example")),
         body: Column(
           children: [
              CenteredGrid(
               itemCount: imageUrls.length,
               crossAxisCount: 3,
               crossAxisSpacing: 12,
               mainAxisSpacing: 8,
               itemBuilder: (context, index) {
                 return Image.network(imageUrls[index]);
               },
             ),
           ],
         ),
       );
     }
   }
   

2. Output:-

   enter image description here