Keep dotting your i's and crossing your t's until you're out of school. Honestly, if you're above the work, you should blow through it without too much trouble. It's designed to be doable in a reasonable amount of time for someone who is in the same position as you except that they are just coming to terms with the material. You should be able to do it in half the time. If not, then you benefited from the practice.
Once you're doing real work, turning down work will not make you lazy; it will be an opportunity to say, "Sure, I might be able to assist you with that, but you will have to talk to <important person> and <other important person> about the impact on my work on <important project> and <other important project>."
"Oh... no chance of my project taking priority over those. Shoot, and I really need it done this quarter."
"I think <junior developer> can do the job for you. He might need a little guidance, but if he does, I will be happy to make myself available to answer his questions and point him in the right direction."
"Wonderful, thank you!"