In the given sentence, the correct word to use is "quickly." This is because "quickly" is an adverb that modifies the verb "finishing." Since "finishing" is a verb, we need an adverb to modify it. "Quick" and "as quick" do not fit well in the sentence because they are adjectives that describe nouns, not verbs. "So quick" might work, but it would change the meaning of the sentence slightly, emphasizing the speed of finishing rather than its importance. So, to maintain parallelism and correctly modify the verb "finishing," the correct choice is "quickly."
