Since you agreed to the settlement and signed the release, you can't get any additional money.  The fact that the release wasn't notarized is irrelevant.  In exchange for receiving the settlement check, you signed a release which gave up any and all claims you had against the at-fault party in your auto accident.If you had not agreed to the settlement, you could have continued negotiating with the insurance company for additional compensation.  If you were dissatisfied with settlement offers, you could have rejected the settlement offers and filed a lawsuit for negligence against the at-fault party/registered owner of the vehicle.  Once the case is settled, it is too late to file the lawsuit and nothing further can be done.