She's most definitely NOT going to expose you, for her own sake. If you're 16 and she posts your pictures online, it's two federal crimes. Blackmail, and distribution of child pornography.
Those things are usually just fucking scams to scare people dumb enough not to know better. If they expose you than they definitely don't have a chance for more money, right? It's not worth their time in their eyes to go through the trouble when they can just see if the next submissive guy in line is gullible enough to fall for it.
You did the right thing. Block her. Report whatever profile you found her on. Forget anything ever happened.