How will I know when I'm done?

I have finished my Advanced Fiction Writing course without advancing my novel one sentence.

The problem is, I can't do the beginning. When it was a movie, I knew what scene would play as the title and stars' names scolled by, but that scene doesn't seem to work in the novel.

In the middele of writing that last sentence, I got an image in my head of a man leaning on a counter talking to the receptionist at the used car lot. That wasn't what I had envisioned as the scene starting the movie, but maybe that's where Herb should be when the novel begins.

Blast this indecisiveness! I can't even decide if I'm writing a movie or a book, so how can I decide on a beginning?

This is a paragraph I used in the AFW lesson on settings. Do you think this would be a good beginning? Would it make you want to read more, or proclaim, "Bore-ring!"

As Herb approached the used car lot, he cringed, as usual, at the site of the garish turquoise paint peeling off the office wall. Faded plastic pennants fluttered halfheartedly over the dusty cars whose best days were miles behind them. He sidestepped around the broken curb as he bent to pick up some empty pop cans and candy wrappers. "Those young salesmen don't have any respect for this place," he thought to himself wearily. "And why should they?" he added as he surveyed the general shabbiness of the lot.