Jim is angry at Huck not for lying, but for failing to imagine the consequences of his lies, and, more generally, for failing to imagine how he (Jim) experiences the world. Jim was worried to death for Huck, even like a family member would worry, but Huck can’t imagine that and sees only a cheap opportunity to trick Jim in the style of Tom Sawyer. But after Jim expresses how much he worried over Huck, Huck realizes how calloused he’s been, and, as he will later in the novel to an even greater extent, he treats Jim like the equal that he is. That Huck feels no regret for apologizing shows his willingness to cross the slave/white divide and to see Jim as a true human being.