The Work Was to Have Been Done

Today, I learned about infinitive in my grammar class. I couldn't figure out one sentence, and I asked teacher if it was grammatically wrong. Actually, it was a correct sentence. I thought I still didn't know many grammar. :P
This is the sentence I didn't get.
"The work was to have been done, but that seems not to have happened."

I had never used this expression before, so I practiced this grammar and wrote some examples during break time. Then, I asked my teacher if my sentences were correct after class.
ex) The class was to have finished at 10:30, but it didn't.
ex) The homework was to have been finished by noon, but it wasn't.
ex) The essay was to have been written by 10:00, but it wasn't.
ex) My goal was to have been accomplished last year, but it wasn't.
ex) The application form was to have been filled out yesterday, but it wasn't.

I think I understand this expression, and I can use it from now on. :) However, my teacher said this was not common expression. He recommended me that using "should" or " be supposed to" instead of infinitive to be safe.
ex) The class should have been finished at 10:30, but it didn't.
ex) The class was supposed to be finished at 10:30, but it didn't.
Yeah, I know. However, I want to learn any expression. Regardless of difficulty, I want to know every grammar rule because I don't want to misinterpret by lacking knowledge.
My teacher asked me if I was planing on taking college level academic writing class. I told him I should give up continuing to take advanced writing class next semester, I would take grammar class though because I was not planing on entering a university, and it's time to focus on studying for NCLEX. I'd like to take NCLEX next year. I wish I would take writing class and master writing essay. However, I should change my schedule next semester. Hmm... Frankly, I really have a desire to study writing now and I may not be able to resist the temptation... but I should focus on NCLEX for now.
I might say next semester, "My taking writing class was to have been finished, but I couldn't stop studying writing essay."