When Godot exports a project it outputs a .exe and .pck files, you need to place those two files into the same folder, compress that and then upload that as the game. I'm pretty sure that the .pck file holds all of your data (sprites, sounds, scripts, etc.). If you're using C#, then there will be some additional files exported along with the exe and pck, include those too. An application (exe) file is not standalone.