As a language model AI, I can help you with creating the basic structure of a game creation app using HTML and JavaScript. Below is an example of how the code structure for the app could look like. Keep in mind that this is just a skeleton code, and you will need to add further functionality and design to make it a complete and polished game creation app.
Please note that this code is just a starting point, and you will need to add more functionality, styling, and improve the user experience to make it a fully functional app.
Remember to save the above code in a single HTML file, then you can open it in a web browser on your smartphone to play around with the game creation app.