The neutral pigtail of the breaker should be connected to the neutral of the incoming power.
The neutral of the outgoing power (if any) connects to the neutral lug on the breaker.
The breaker may still work as a switch and maybe even as an over-current protection, without the GFCI function working. But there is no easy way to test that it is working for over current. It should really be replaced - you let the magic smoke out.