My teacher must think that I'm someone else.
What makes you think that your teacher believes you're someone else?
I just have this weird feeling that they do.
If someone thinks you're someone else then you should correct them right away. If you don't let them know, then you're impersonating someone else and when they find out they're going to be very disappointed in you.
I just don't know what to say.
You can start by introducing yourself by your full name. See what their response to that is. If they are surprised then follow up from there.