Please delete your Saved and Intermediate folder from your project. Once you’ve done that, go into your struct ‘LevelData’ and fix the conflict with the class name. The UnrealHeaderTool also had an issue with the target ‘GunRail’, check that out too. After you’ve fixed each issue, try to package to make sure no more pop up.
UATHelper: Packaging (Windows (64-bit)): UnrealBuildTool: C:/Users//Desktop/GunRail/Source/GunRail/LevelSelect.h(26) : Error: struct: 'LevelData' conflicts with class name
UATHelper: Packaging (Windows (64-bit)): UnrealBuildTool: Error: UnrealHeaderTool failed for target 'GunRail' (platform: Win64, module info: C:\Users\\Desktop\GunRail\Intermediate\Build\Win64\GunRail\Development\GunRail.uhtmanifest, exit code: OtherCompilationError (5)).