Truthfully, No one should ever found out unless you are a minor. So perhaps you are?

But when they get over the initial “disappointment”, they should be very proud of you for taking care of yourself.

I don’t think you have a problem with using a family plan “without permission”. You are either covered or you or not… And obviously you were covered, I am assuming?

If there was a huge deductible that had not been met yet, though, I guess they could’ve ended up with a large bill. Or if you were simply not on that plan but they thought at the drs office that perhaps you were? Idk.

The only problem related to “getting into trouble” would be if you misrepresented who you were when you went to the doctors appointment itself.

If they would charged a lot of money, you can always offer to pay it back to them. If it is just a moral issue, that is more tricky… But most parents would be proud that you were trying to take care of yourself and be safe.