I got my period on dec2nd ended on the 7th then blood again on the 11th i don't understand?

Happens to everyone : It is not rare at all for someone to have an off period from time to time. In your case the bleeding just lasted a little longer than you expected. This is very normal and usually corrects itself over the next cycle or two. If the long periods continue then schedule a visit with your doctor to discuss methods to minimize menstrual bleeding.