This is not normal, but it is understandable. It sounds like someone broke communication somewhere. Somehow, someone got the idea that you were an ML expert, and they hired you based on that, even though you told them specifically in the interview that you're not. Did you imply something like that on any supporting documents you gave them (e.g. your resume)?
You need to fix this miscommunication. When you say "my manager told them I was a machine learning expert", who is "them"? I think that person is the one you need to have a serious chat with. You need to tell that person that your manager was mistaken when he told them that, and you do not have as much expertise as was advertised. As a result, you aren't comfortable with the responsibility you've been given.
Be aware that this might get you fired, but this is a question you need to ask yourself: Would you rather be fired, or would you rather your "crowning achievement", so to speak, of your internship being a garbage fire? It's a hard choice, but it's one that it seems you have to make. The difficulty being that, as this is an internship, you'll need to find an alternative internship, which adds additional headache to the situation.
Overall, this is a really bad situation that you shouldn't have been put in. Someone dropped the ball, and you're on the hook to fix it.
Aside from all of this, it's not normal for an intern to lead anything. It sounds like your company wanted to get some cheap labour from someone with expertise without hiring someone who actually has that competency, and they got you, which is to say they got what they paid for. Even aside from all of the other concerns, it is definitely not normal for an intern to be given leadership responsibilities, except, occasionally, perhaps, if the entire project is intern-developed, and even then not usually.