Any God worth believing in, and we believe our God is just that, knows you better than you know yourself, and loves you more than you love yourself. That God isn't waiting for you to screw up so he can send a runaway train to kill you so he can laugh as he burns you in hell. That is no God at all.
Pray to God for the grace to live according to his commandments generally, and especially to struggle against the particular sinful tendencies you may have. Begin to do the hard work of living according to the gospel. Entrust yourself to his mercy, always to his mercy. He knows what he is doing, and eventually he'll convince you of that as you grow in your relationship with him. Many times, these fears come from our own "ignorance" of God, but as we grow in our relationship with him, as we get to know him better, love drives away fear.
And stay close to Mary.