The builder has to give the completion certificate and should handover possession only after the CC is given.
In fact you should not have occupied the premises without getting the completion certificate because it is not advisable to occupy the incomplete building/flat.
However, at this stage you can d nothing to rectify yor mistake except to issue a legal notice to the builder pointing out his deficiency in service and demand him to complete the same immediately or else to face the music of law. You can even demand the car parking space to be allotted to you as per the sale agreement
If the builder is not complying with the demands made then you may decide to aproach consumer court for relief and remedy.
The owners to sit and decide about the sharing of expenses of common utilities like lift, bore well, water motor.
The sharing of expenses should be based on number of units and by number of owners.