An occasion when I arrived early

A course (building?) at my university was under construction. The teacher (of the course) is also the dean of our college. We usually go to the/arrive at the classroom ahead of time. The class is the first lesson on Wednesday afternoons. One time, I arrived at the classroom, but nobody was there. I thought I was in the wrong classroom because the teacher and the students were not there. I did not go inside (the classroom). But then, the dean appeared. He saw me and asked  what happened because there was no one inside the classroom/no one showed up/no one turned up/the classroom was empty. 

Let me explain what happened. We had to hand in/submit our drawings on Thursday. Many students spent a lot of/lots of time completing their drawings. Since there are 70 students in the class, everyone thought that the absence of one person would not be noticeable. But I did not expect that no one would show up to class except me! The dean was angry when he heard my explanation. I called my classmates to let them know and told them to quickly come to class. After about twenty minutes, other students came/started to come. This was an occasion when I arrived early but had a horrible experience. I faced the angry dean alone for twenty minutes.