Question

The test was difficult; it was poorly written, and lengthy. Is this a parallel sentence?

Answer 1

This might help you: http://examples.yourdictionary.com/parallel-structure-examples.html

A parallel sentence generally lists three things
Like: She likes to bike, read, and swim.
An incorrect example would be: She likes to swim, biking, and to read.

Hope that makes sense and helps :)

Answer 2

That said, I do not think your sentence is a parallel sentence.