【Docker × Rails】コンテナ上にdb:create実行時、Access denied for userが発生する

Question

初学者です。
既存のrailsアプリにdockerを導入時、

$ docker-compose run web bundle exec rake db:create

を実行すると

Creating my_app_web_run ... done
Access denied for user 'user'@'172.18.0.3' (using password: YES)
Couldn't create 'my_app_development' database. Please check your configuration.

というエラーが発生します。
原因が特定できず、困っています。

#ファイル設定

FROM ruby:3.0.2
RUN curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | apt-key add - \
    && echo "deb https://dl.yarnpkg.com/debian/ stable main" | tee /etc/apt/sources.list.d/yarn.list
RUN apt-get update -qq && apt-get install -y build-essential libpq-dev nodejs yarn


WORKDIR /my_app
COPY Gemfile /my_app/Gemfile
COPY Gemfile.lock /my_app/Gemfile.lock
RUN gem install bundler
RUN bundle install
COPY . /my_app

RUN yarn install --check-files
RUN bundle exec rails webpacker:compile

# Add a script to be executed every time the container starts.
COPY entrypoint.sh /usr/bin/
RUN chmod +x /usr/bin/entrypoint.sh
ENTRYPOINT ["entrypoint.sh"]
EXPOSE 3000

CMD ["rails", "server", "-b", "0.0.0.0"]

#docker-compose.yml

version: "3"
services:
  db:
    image: mysql:8.0.26
    environment:
      MYSQL_ROOT_PASSWORD: password
    ports:
      - "3306:3306"
    volumes:
      - mysql-data:/var/lib/mysql
  web:
    build: .
    command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
    volumes:
      - .:/my_app
    ports:
      - "3000:3000"
    depends_on:
      - db
    stdin_open: true
    tty: true
volumes:
  mysql-data:
    driver: local

#entrypoint.sh 

#!/bin/bash
set -e

# Remove a potentially pre-existing server.pid for Rails.
rm -f /my_app/tmp/pids/server.pid

# Then exec the container's main process (what's set as CMD in the Dockerfile).
exec "$@"

#database.yml

default: &default
  adapter: mysql2
  encoding: utf8mb4
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
  username: root
  password: password
  socket: /tmp/mysql.sock
  host: db

#試したこと

①root パスワードの確認

$ mysql -u root -p

# environment:
  MYSQL_ROOT_PASSWORD: password
  ここに設定してあるpasswordで入れました

②userのmysql接続を許可

mysql> RENAME USER 'user'@'localhost' to 'user'@'%';
Query OK, 0 rows affected (0.02 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)