InteractiveViewer image is zoomed in

You need to use a TransformationController to control InteractiveViewer. Here is the code:

  TransformationController _controller;
  @override
  void initState() {
    _controller = TransformationController();
    _controller.value = Matrix4.identity() * 0.5;
    super.initState();
  }
  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Container(
        height: 350,
        child: InteractiveViewer(
          transformationController: _controller,
          minScale: .1,
          maxScale: 1,
          onInteractionEnd: (s) {
            print(_controller.value);
          },
          constrained: false,
          child: Stack(
            children: [
              Image.asset(
                "assets/Big.Buck.Bunny.-.Landscape.png",
                fit: BoxFit.fitWidth,
              ),
            ],
          ),
        ),
      ),
    );
  }

Please note that you may need to adjust initial scale value(the one multiplying with Matrix4) to get your desired output.