I had a small cut on my finger & touched a glass with my teacher's blood on it. (it was part of biology class, we learned about blood) can i get hiv?

Inform school/family: Even if you are 18 and of legal age. Inform parents/teacher/doctors all or some you are. The exact scenario you describe is not well described but the literature on needle sticks tell us that HIV risk is about 3/1000 incidents. A important factor is whether HIV exists prior to this and thus for an exposure testing of all subjects is recommended. School, public health departments have guidelines.