Why are my pictures overexposed? - 1

I've been taking pictures with my Nikon D3100 using my new prime lens (35mm F1.8). When I took pics today I noticed many of the pics were overexposed. All pics were taken using aperture priority mode, mostly portraits shots of my daughter and her friends at the local outdoor mall. The pics were taken around 7-8pm so the light wasn't harsh. Also many of the pics were shot at the smallest aperture setting, either F1.8 to F2.2.

What am I doing wrong?

I think you would get a better answer to your question if you posted your question in the camera section. This section is mainly about email and attaching pictures to email.
here is the link to the camera section.