Pump won't shut off

I just installed a new pre-charged tank. When I filled the system with water to prime, the pressure gauge rose to 45psi (with pump off). When I plugged the pump in, the pressure rose to 50+psi but just keeps on running (cutoff is 50). Any ideas? Thanks!

The switch should shut off the pump at 50 psi, so your gauge is wrong or the setting on the switch needs adjustment. That assumes you actually primed the pump and got water all the way down the drop pipe to the foot valve. If not the pump isn't getting water because it isn't primed right.

How did you prime to get 45 psi on the gauge? Usually there is no pressure when you prime.