There is (as you describe your process) no validity to anyone's saying you are guilty of plagiarizing "Walk on the Wild Side." As you describe your process, it's more likely that Lou Reed copied the same song that you did. Either way, just document your process, and proceed. It's unlikely that anyone ever asks you to "cease and desist," and if they do, you can always decide to contest it or give in at that time. I wouldn't let it become an issue (in my mind) until it became an issue outside of my mind.