I wouldn't worry about it - you'd be surprised how many new users post questions and army lists in the introductions section
Just make sure going forward that you try and post in the correct threads / sub forums from now on.
If you are really bothered about your introduction thread, you can edit the post (however, be aware that will make all of the replies not make sense!) or you can report the post (little yellow triangle) and report the thread to a Mod and see if they think it needs to be deleted or moved.