#2 is active (the other two you have correct).
In #2 the sentence is about "We" and the verb is "having fun". It is "We" who are doing the "having fun". So this is an active voice.
In #3 the sentence is about "The cars" and the verb is "parking". But it isn't the cars that are doing the "parking", some other unmentioned person is doing the action of parking, the cars are just passively being parked. So #3 is passive voice.
If course, in #1 the sentence is about "I" and the verb is "being stupid", this is active voice because it is "I" who am actively being stupid.