If you haven't been actively engaging in any sexual activity you should be ok. There are 5 weeks in this month. This can sometimes throw your cycle off by a week. I wouldn't worry right now. If things persist and it goes missing for like a month or two you may want to talk to your parent and make sure all is well. Some women do experience irregular menstrual cycles but not sure at what age something like this happens.
But I'm betting it will be here in the next couple days
Don't worry it takes a few monthes/years for your period to happen consistently although if you don't have your period in a few days maybe talk to your doctor
Ur period is not always going to Be on time there is nothing to be worried about!