I was hoping for more information before I composed an answer, but if this doesn't address what you wanted to find out, you can respond here to this question thread and provide me with the information I asked for in the first place, and I can refine my answer accordingly.
There is a very popular online scam which has come to be known as "sextortion," a shorthand for sexual extortion, and this sounds like this may be what's going on here. Unscrupulous people hover around on chat rooms and dating sites, and they lure in their victims by assuring them that they are of age but then engaging them in sexual chat and/or pictures. Then, all of a a sudden, the unsuspecting victim is told that the girl is still a minor.
Sometimes, as in your case, she tells you that herself. Sometimes, you don't get the news until hours later or the next day when you get a phone call from a supposedly angry authority figure. And what that authority figure typically wants is money or he claims he'll prosecute. That's blackmail, and one should never give into that.
If that's what happened, you need to block all contact with the so-called minor and her so called counselor and send no money . You should never give in to an extortion request. If you pay them, you'll have to keep paying them for the rest of your life. They only have power over them if you give in to them.
In these scams there really isn't any minor at all. It's all just a way to intimidate you to get money. If you simply disappear the way you did, the scammers go away and move on to someone else, because it's not about reporting you but only about money, so they can't really report it without producing the minor and swearing out a complaint with the police. Scammers don't do that.
To be on the safe side, however, if you have your copy of the text thread, it's got evidence where you've specifically said that you were not interested in anyone underaged. You may want to print that up and keep it somewhere if you still can, because it may be helpful down the road.
To recap -- the chances are very high that there's no real minor here, no real counselor, and nobody who would dare go to the police. You've already blocked their contact. You should also cancel your membership on the dating website.
The odds are high that nothing at all will happen except that they will move on and try to set someone else up for extortion. The sudden appearance of her "counselor" in the midst of your conversation is so suspicious as to be downright unbelievable. I cannot guarantee you that you have nothing to be concerned about, however. So in the event that you hear from someone who claims to be a police officer, or if the minor or her counselor try to reach you some other way, say NOTHING about this incident to the police except that you do not wish to discuss anything until you can reach your lawyer. That's your right and the authorities are required to honor that and can't hold that against you. Then you can go out and look for a local criminal lawyer.