How does one get 'salvation?'
As Christians we believe we have our salvation because of Christ's death on a cross for us. Some people think you must accept Jesus as your personal savior and say a certain prayer to be "saved" while others believe it is Baptism when you reach an age where you can make the decision yourself.
As Catholics we believe that at our Baptism we are incorporated into the mystical body of Christ; baptized prophet, priest, and king; and are radically configured to Christ. We become members of the Church and as such salvation is ours.
Can we refuse salvation? I believe we can. Salvation is a gift, like mercy and grace. While we are here on earth we can opt to live in way that is incompatible with our Baptism and so in a sense, reject salvation. Once we die, and meet God we can also reject salvation. Our free will does not leave us. Though God has infinite mercy and wants us to be with Him, would He not let us choose hell as opposed to eternal life with Him? Of course, how could one not choose eternal life in heaven when in the presence of God.