You can use Spacer() widget. Just like below
ClipPath( clipper: RoundedDiagonalPathClipper(), ... child: Transform.scale( ... child: Container( ... child: Form( child: Padding( padding: const EdgeInsets.all(8.0), child: Column( children: [ ...

Spacer(),

Align( alignment: Alignment.bottomRight, child: IconButton( onPressed: () { controllerV.nextPage(duration: Duration(milliseconds: 750), curve: Curves.easeIn); }, icon: Icon(Icons.expand_circle_down)), ),

Or You can give height to the container. And you code will work

If anybody is looking for complete circular button then I achieved it this way:
Center( child: SizedBox.fromSize( size: Size(80, 80), // Button width and height child: ClipOval( child: Material( color: Colors.pink[300], // Button color child: InkWell( splashColor: Colors.yellow, // splash color onTap: () {}, // Button pressed child: Column( mainAxisAlignment: MainAxisAlignment.center, children: <Widget>[ Icon(Icons.linked_camera), // Icon Text("Picture"), // Text ], ), ), ), ), ), )