I bet you had a positive effect on more people who witnessed that, than you realize. For some of them, your voice will be a memory that they will take with them for the rest of their lives. I know that sounds a little dramatic, but it's not. You never know when the memory of your voice belting out that song in the middle of those circumstances, in that store, may come to mind for someone and help give them a little push of strength to stand up for their own rights in some future situation.