Undergrad Negative values for Gaussian Distribution

[aron silvester]

So in my Physics lab, we divided into groups and our task was to throw darts on a target containing 13 bins. The bins look something like the image below. At the end, our class combined our average, standard deviation, and standard error. I made a Gaussian Distribution and I noticed that the third standard deviation below the mean of 7.22 is equal to -0.88. Is this possible to have a negative value even though there were only 13 bins?

Class Data:
Average: 7.22
Standard Deviation: 2.7
Standard Error: 0.085

Here is the target. It was just a paper that we pinned to the wall.

Here is the Gaussian Distribution that I created with the negative value.

 

[NFuller]

Since you have labelled the bins left to right in order, the number can be thought to measure distance from the origin where the origin is one box to the left of box 1. There is nothing wrong with the distribution. Its telling you that there is some finite probability that someone is really bad at aiming and throws a dart which lands to the left of box 1.