Blotchy spots on chest and stomach

I'm 19 years old. I have recently started getting smooth blotchy spots on my chest and it's beginning to go to my stomach. The rest of my skin is fairly tan and the spots are a lighter color. The spots started occurring after I was out in the sun for many hours for a few consecutive days. I had an even tan for a while then the spots appeared. I'm scared that I may have done some serious damage to my skin. Also, the spots are very embarrassing as you can see them when I wear a low cut top. Please help.