Flutter – how remove padding from BottomNavigationBar?

I made a sample code using your part code.

But I can not reproduce like your problem with shared your code.
Could you share a part of Scaffold’s bottomNavigationBar or other related to code.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Text(
                'You have pushed the button this many times:',
              ),
              Text(
                '$_counter',
                style: Theme.of(context).textTheme.display1,
              ),
            ],
          ),
        ),
        bottomNavigationBar: BottomNavigationBar(
            selectedFontSize: 0,
            type: BottomNavigationBarType.fixed,
            currentIndex: 0,
            items: [
              new BottomNavigationBarItem(
                icon: _buildIcon(),
                title: SizedBox.shrink(),
              ),
              new BottomNavigationBarItem(
                icon: _buildIcon(),
                title: SizedBox.shrink(),
              ),
              new BottomNavigationBarItem(
                icon: _buildIcon(),
                title: SizedBox.shrink(),
              )
            ]));
  }

  Widget _buildIcon() {
    return Container(
      width: double.infinity,
      height: kBottomNavigationBarHeight,
      child: Material(
        color: Colors.grey,
        child: InkWell(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              Icon(Icons.email_outlined),
              Text('111', style: TextStyle(fontSize: 12, color: Colors.white)),
            ],
          ),
          onTap: () {},
        ),
      ),
    );
  }
}