Flutter create→flutter run でビルドエラー

現在開発中のFlutterアプリとは別のアプリを開発しようと、
AndroidStudio→File→New→NewFlutterProjectからアプリを作って走らせるとエラーになりました。

エラー内容

$ flutter run
Using hardware rendering with device Android SDK built for x86. If you get graphics artifacts, consider enabling software rendering with "--enable-software-rendering".
Launching lib/main.dart on Android SDK built for x86 in debug mode...
                                                                        
FAILURE: Build failed with an exception.                                
                                                                        
* What went wrong:                                                      
A problem was found with the configuration of task ':app:processDebugResources'.
> File '/Users/aaaaaaaaa/Library/Android/sdk/platforms/android-28/android.jar' specified for property 'androidJar' does not exist.
                                                                        
* Try:                                                                  
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
                                                                        
* Get more help at https://help.gradle.org                              
                                                                        
BUILD FAILED in 10s                                                     
Running Gradle task 'assembleDebug'...                                  
Running Gradle task 'assembleDebug'... Done                        11.2s
Gradle task assembleDebug failed with exit code 1

$ flutter doctor -v
[✓] Flutter (Channel dev, v1.14.6, on Mac OS X 10.14.6 18G2022, locale ja-JP)
    • Flutter version 1.14.6 at /Users/aaaaaa/flutter
    • Framework revision fabeb2a16f (8 days ago), 2020-01-28 07:56:51 -0800
    • Engine revision c4229bfbba
    • Dart version 2.8.0 (build 2.8.0-dev.5.0 fc3af737c7)

 
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.3)
    • Android SDK at /Users/aaaaaaa/Library/Android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-29, build-tools 29.0.3
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 11.3.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 11.3.1, Build version 11C504
    • CocoaPods version 1.8.4

[✓] Android Studio (version 3.5)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 43.0.1
    • Dart plugin version 191.8593
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)

[✓] Connected device (1 available)
    • Android SDK built for x86 • emulator-5554 • android-x86 • Android 10 (API 29) (emulator)

• No issues found!