text: You are correct, each individual should make an informed decision for herself whether she should call herself a Catholic or not.
  The Catechism of the Catholic Church is posted on line for everyone to become informed on what it means to be a Catholic.  Every person who calls herself a Catholic is expected to be at least aware of these positions.  By calling your self a Catholic you are proclaiming that this is what you believe.
  I suggest you look up abortion in the CCC and determine if you agree with Church's position. Then you should look up other hot-button issues and determine the Church's position on those.
  Then you can decide for yourself if you want to continue to call yourself Catholic or not.
  And to answer your question as who gave the Church that authority to determine what it means to be a Catholic, it was Jesus Christ.