Hi,
This would just be the spot of inflamed skin where the burn was. Skin cancer cannot show up immediately after a sunburn, not in such a short duration.
A sunburn is a burn to living tissue such as skin produced by overexposure to ultraviolet (UV) radiation, commonly from the sun's rays.
sunburn and the increase in melanin production (as in a tan) are both triggered by direct DNA damage. When the skin cells' DNA is damaged by UV radiation, cell-death is triggered and the skin is replaced.
Malignant melanoma may occur as a result of indirect DNA damage if the damage is not properly repaired. Proper repair occurs in the majority of DNA damage, and as a result not every exposure to UV results in cancer.
The best treatment for most sunburns is time. Given a few weeks, they will heal including the blisters.
The skin can be hydrated by applying topical products containing Aloe vera and/or vitamin E, which reduce inflammation. Hydrocortisone cream may also help reduce inflammation and itching.
ref:http://en.wikipedia.org/wiki/Sunburn