Bullseye is right, replace it. Call Ruger parts, they will send you a new one. You can also order firing pin springs for 1.15 each from Numrich (order something else to justify the 4.65 shipping). The new spring will only fit over the plunger one way. The "hook" on the plunger faces down, all the way forward into the recess under the firing pin.
Since the spring is broken, your firing pin stop pin will be loose and want to fall out when you take out the bolt. Don't lose it.