Remove space around an image flutter

Question

Hello im making an app where I have an image from the camera with a send button. Around the image is much space and if the image's height is less than the send button isnt at the bottom anymore. I need the image vertically centered and a maximun width. The Message container should be on the bottom. Thanks for your help.

This is the code of my app:

return Scaffold( 
resizeToAvoidBottomInset: false, 
body: Stack( 
alignment: Alignment.bottomCenter,
 children: [ 
Image.file(widget.image,), 
Container( 
child: Row( 
children: [ 
Expanded( 
child: Container( 
margin: EdgeInsets.all(3), 
height: 50, 
child: TextField( 
controller: _writeMessageTextEditingController, 
style: TextStyle(
color: Colors.white), 
decoration: InputDecoration( 
contentPadding: EdgeInsets.only(left: 15, top: 15,), 
border: OutlineInputBorder( 
borderRadius: BorderRadius.circular(300), 
borderSide: BorderSide( 
width: 0, 
style: 
BorderStyle.none, 
), 
), 
focusedBorder: OutlineInputBorder( 
borderRadius: BorderRadius.circular(300), 
borderSide: BorderSide( 
width: 0, 
style: BorderStyle.none, 
), 
), 
filled: true, 
hintStyle: TextStyle( color: Colors.grey, ), 
hintText: "Message", 
fillColor: Colors.grey[800], 
), 
), 
), 
), 
Container( 
margin: EdgeInsets.all(3), 
height: 50, 
width: 50, 
decoration: BoxDecoration( 
borderRadius: BorderRadius.circular(100), 
color: Color(0xff0077b6), 
), 
padding: EdgeInsets.all(8), 
child: GestureDetector( 
child: Icon(
Icons.send, 
color: Colors.white,
), 
onTap: (){ 
String message = _writeMessageTextEditingController.text.toString(); 
File file = widget.image; 
print(file); 
print(message); 
_writeMessageTextEditingController.clear(); 
Navigator.pop(context); 
//send message to server 
}, 
), 
), 
], 
), 
), 
], 
), 
);