Could it be Skin cancer?

Hi I am a 13 year old girl with skin that doesn't burn to easy, light brown hair, and blue green eyes. About two days ago I noticed a brownish mark on my mid chest area. I have been looking into skin cancer stuff a lot lately because there is also pinkish mark on my leg that I'm get checked out in about two weeks. But this brownish mark on my chest is freaking me out. Could it be melanoma? I don't ever go tanning and rarely get burned, I don't think I have ever been burned on my chest. Could this just be a scar from a zit or something? (I have a lot of acne on my chest neck area at times)