Have you created a version within it? There’s an issue where if you create an extension but don’t create any versions then you can’t delete the extension, which to resolve you simple create a version like 0.0.1 and then you can delete.
If that’s not your particular issue you’ll have to give more info when you say “unable to delete it”, such as what happens when you try? Do you get an error? Does anything get thrown in console?