I actually noticed the opposite pattern: about 95% of the time, the double-check caught careless mistakes and I ended up with a higher score for it. Perhaps it was because of my typical test-taking strategy: I'd race through the questions and answer every one immediately, then I'd go back and double-check all the steps to make sure I hadn't done anything silly.

I did notice that my score tended to decrease if I triple- or quadruple-checked my answers, though.