Read it.
Per the catechism, you cannot know whether you are going to heaven or not. If you knew you would die tomorrow, the church could not tell you if your salvation was assured (per its own doctrine). If you say you do know as a Catholic, you are outside of your churchs teaching.
Jesus brought the good news, He died for humanitys sins, and the Bible says that we can know that we are saved from hell.
There was a point in my life when I knew I was going to hell. I knew it. I had not accepted Jesus, and I knew my fate was hell. Oh, I was Confirmed, I went to mass every Sunday, I said the rosary, I had my prayer cards, I had my metals of a saint that I wore. But I didnt have Jesus Christ as my redeemer. I was going to be one of the ones that He said, I never knew you to.
I once asked a Catholic priest if I could be sure that I was going to heaven. Do you know what he told me? He stammered, paused a long time, looked at his shoes, and said to me: well, that is a great mystery.
My sins are forgiven. Its not that Im perfect, or that Im better than anyone else. But no one can snatch me from Christs hand. And I know Im going to heaven. The question you need to ask yourself is: are you sure? If not, would you like to be?