Flutter: How to place an Icon on a CircleAvatar and center it?

I want to center the camera icon but i couldnt do it. I tried to use an image instead of an icon but this still didnt work. I think it doesnt work because it is not possible to place an icon on a CircleAvatar but there must be a way to this. Here is my Code:

    return SizedBox(
      height: 115,
      width: 115,
      child: Stack(
        clipBehavior: Clip.none,
        fit: StackFit.expand,
        children: [
          CircleAvatar(
            backgroundImage: AssetImage("assets/images/Profile Image.png"),
          ),
          Positioned(
              right: -16,
              bottom: 0,
              child: SizedBox(
                  height: 46,
                  width: 46,
                  child: FlatButton(
                    shape: RoundedRectangleBorder(
                      borderRadius: BorderRadius.circular(50),
                      side: BorderSide(color: Colors.white),
                    ),
                    color: Color(0xFFF5F6F9),
                    onPressed: () {},
                    // TODO: Icon not centered.
                    child: Center(child: Icon(Icons.camera_alt_outlined)),
                  )))
        ],
      ),
    );

Widget build(BuildContext context) {
    return SizedBox(
      height: 115,
      width: 115,
      child: Stack(
        clipBehavior: Clip.none,
        fit: StackFit.expand,
        children: [
          CircleAvatar(
            backgroundImage: AssetImage("assets/images/Profile Image.png"),
          ),
          Positioned(
              bottom: 0,
              right: -25,
              child: RawMaterialButton(
                onPressed: () {},
                elevation: 2.0,
                fillColor: Color(0xFFF5F6F9),
                child: Icon(Icons.camera_alt_outlined, color: Colors.blue,),
                padding: EdgeInsets.all(15.0),
                shape: CircleBorder(),
              )),
        ],
      ),
    );
  }

I've removed the SizedBox and used a RawMaterialButton instead.