You become a Christian by simply putting your trust in Jesus and His sacrifice for you on the cross. There is no "trying" involved. If you trust Jesus and if you ask Him to forgive you of your sins and be your Savior, then you are a Christian. It is living like a Christian after you've become one, that is difficult.
If you believe that in order to become a Christian you must be good, then you misunderstand or don't have a good understanding of salvation. A Christian is a Christian by the gift of God (Rom. 6:23), not the work of man (Eph. 2:8-9). There is nothing you can do to earn salvation or keep salvation. It is simply something God freely gives you. If you want it, confess your sins, repent, turn to God, and trust Jesus as your only Savior. Then, and only then, will you become a Christian.