Developing for different screen sizes using flutter?

I have an app that I am going to upload to the appstore and playstore pretty soon but I am worried that it might look funny on different phone screens that vary in sizes (The app is for mobile phones only no tablets) what's the best way to code for different screen sizes using flutter?

Try using LayoutBuilder for different layout size and OrientationBuilder for different orientation.

Check this: https://medium.com/flutter-community/developing-for-multiple-screen-sizes-and-orientations-in-flutter-fragments-in-flutter-a4c51b849434