Because it's an autoflowering and they start to bloom from around 4 weeks, some a little earlier, some a little later, it depends on your care.
Stress from some neglected factor can trigger early flowering, still, if you're starting to see the pistils, I don't see anything wrong with it.
Have you grown auto before? Could you add a photo so we can better see what the problem might be? Maybe it doesn't have any.