NavBar and Drawer Flutter

I want the navbar inner container to take 80% of screen width... is that possible with the AppBar Widget?
This means that i want the hamburger icon on the right (generated by endDrawer) to move 10% to the left

import 'package:flutter/material.dart';

class Navbar extends StatefulWidget {
  const Navbar({Key? key, required this.child}) : super(key: key);
  final Widget child;

  @override
  State<Navbar> createState() => _NavbarState();
}

class _NavbarState extends State<Navbar> {
  final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: scaffoldKey,
      endDrawer: Drawer(
        backgroundColor: kYellowColor,
        child: Column(
          children: [
            Text('Form'),
            Text('Receipt'),
          ],
        ),
      ),
      appBar: AppBar(
        backgroundColor: kYellowColor,
        iconTheme: const IconThemeData(color: kBlackColor),
        automaticallyImplyLeading: false,
      ),
      body: widget.child,
    );
  }
}

Here is the current navbar

You can create custom appbar with PreferredSizeWidget.

class MyAppBar extends StatelessWidget with PreferredSizeWidget {
  final Size size;
  const MyAppBar({
    Key? key,
    required this.size,
  }) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Align(
      child: Container(
        color: Colors.cyanAccent,
        width: size.width,
        height: size.height,
        child: Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children: [Icon(Icons.menu)],
        ),
      ),
    );
  }

  @override
  Size get preferredSize => size;// mainly align is handling constraints 
}

And pass size

class _NavbarState extends State<Navbar> {
  final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(
      builder: (_, constraints) => Scaffold(
        key: scaffoldKey,
        endDrawer: Drawer(
          child: Column(
            children: [
              Text('Form'),
              Text('Receipt'),
            ],
          ),
        ),
        appBar: MyAppBar(size: Size(constraints.maxWidth * .8, kToolbarHeight)),
        body: widget.child,
      ),
    );
  }
}