NTA. I can personally relate to not wanting to share some stuff with people I see in real life but would share them with online friends, and vica versa.

You created the IG account to keep in touch with online friends, and later on you let Kate and Dipper see it too.

Dipper was the first to betray you by sending screenshots of your private messages, which is wrong in itself, but you also requested they don't inform anyone of account's existence and Dipper did it anyways.

Jacky's response was also inappropriate. She got mad at you for not sharing what you're not comfortable sharing with her at the moment. She said it's not about the IG account but the more I read the more it became clear she was mad at you for not telling her everything about yourself. She's a control freak in the making, if not one already.

While we can't be sure of it, it looks like Jacky told Kate bad thing(s) about you (which you also pointed out), including lying about you blocking her. In this case, Jacky got the result she wanted and this would match with her being a control freak.

You're rightfully upset and I wouldn't recommend you coming out to Jacky as it will most likely fuel her future malicious actions towards you, such as this one.

Assholes here are Jacky, and Kate for not checking in with you, who's been her friend for a long time, about what she heard and rather acted upon it immediately.

You should cut these two "friends" from your life. I can't share my opinion on Shane as they are barely mentioned.

I hope it all ends well. This must have put a lot of stress on you ❤️