For example:
I had been finishing my exam when my teacher told us to stop writing.
So in this sentence I'd like to say that I was about to finish my exam, but had been interrupted. If I'd like to highlight me finishing the exam in the past(so it was like 95% done and needed a bit more time) and also got interrupted while I was finishing, can I use the sentence mentioned above?
Can past continuous be past perfect continuous in this sentence, or it's obvious which event happened earlier and it doesn't require such grammar? That's what I'd love to know.