Why is "I was immediately fascinated by" translated in the p.c.? To me it is a description of how the person felt, thus I used the plus que parfait.

Hi Ann, 

I think you are confusing the 'imparfait' with the 'plus-que-parfait' which are very different past tenses.

Take a look at the following basic lessons which will have links to others - 

https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-continuous-past-and-past-habit-l-imparfait

https://progress.lawlessfrench.com/revision/glossary/verb-tense-mood/the-french-pluperfect-le-plus-que-parfait

Hope this helps!