Honestly, I think he's struggling with his past and as he stands on judgement day, he tries to call out to God, but he doesn't think that God is big enough to cover his sins (He is) and when he refers to Sunday morning, he means that he feels spiritually dead and he regrets not being strong enough to turn to God, hence the Sunday morning reference to church. And so, although he regrets what he's done, in the end his inability to believe in God's saving grace sent him to hell.
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