I'm a member of CritiqueCircle.com. It's a neat online writing community that allows members to submit an excerpt of their writing for review and critique. I don't post often. Just enough to maintain my membership and get some feedback on pieces of my work.
The majority of members are respectful and polite, and they give fairly good reviews (though I'm still trying to figure out the "dichotomy in the juxtaposition of the opulence" remark) but I was a bit surprised at a couple of comments I received on a recent submission. In one scene, my character woke up after spending the night in a sleeping bag in the back seat of her car. My critiquer got a kick out of my description and said it's clear we've shared similar experiences. Another critiquer seemed to love the police interview I wrote. She asked something along the lines of, "Are you a police officer, or are you married to one or watch a lot of crime shows?"
None of the above. I've never spent the night in the backseat of my car, nor do I know a police officer. (Sadly. I could use their input at times.) I hate watching television, so that rules out crime shows.
I hope my fellow critique buddies will allow their imaginations to go where they've yet to tread. It makes the story more three-dimensional.
So yes, it is okay to make something up when writing a novel.