Norman Greenbaum’s theology is rather odd. “Never been a sinner, never sinned” is just about the opposite of what Christianity teaches.
That’s a pretty jarring line all right. Everything else seems to be OK if not great, and if it went something like “No more a sinner, forgiven for my sin” then it would make the piece pretty well straight on Christian. Even modern Jewish theology acknowledges the ubiquity of sin if not the Fall the way Christians do.