I think if you showed not only the point estimate, but also some measure of uncertainty like standard deviation, it should have given you a passing grade. It's hard to say why an answer like 6.8 +- 5 is wrong.
Even if you don't yet have formal statistical chops, it should be at least possible to show cumulative distribution function of results that will convey the story better than a single answer with overly optimistic implied precision.
Even if you don't yet have formal statistical chops, it should be at least possible to show cumulative distribution function of results that will convey the story better than a single answer with overly optimistic implied precision.