Choice A is the best answer. Akira is very concerned Chie will find his mar-riage proposal inappropriate because he did not follow traditional protocol and use a "go-between" (line 65,"I... time"). This is clear in lines 63-64 ("We... proposal"), when Akira says to Chie "Please don't judge my candidacy by the unseemliness of this proposal."
Choice B is incorrect because there is no evidence in the passage that Akira worries that Chie will mistake his earnestness for immaturity. Choice C is incorrect because while Akira recognizes that his unscheduled visit is a nuisance, his larger concern is that Chie will reject him due to the inappropriateness of his proposal. Choice D is incorrect because there is no evidence in the passage that Akira worries Chie will underestimate the sincerity of his emotions.