The typical way to connect the neutral on 2 pole GFCI breaker is (the line side neutral is usually required for the test function):
Always;
Connect line side white wire (the curly one on the breaker) to the panel neutral
If available;
Connect neutral from the load to the neutral lug on the breaker.
Often the breaker does not require all of the load lugs to be used. You can skip the neutral and even either one or more of the hot legs.
