You were at your school, in your universe. You can chose what you were doing, your classmates names if you want, and stuff like this.

In the MHA universe the 1-A characters were coming back from one of their hang out as a class. While they were walking back to UA, they run into a villain who used their quirk on them, teleporting them to a random other universe.

Your universe.

So they got teleported into your school, in your class.