Your prices do seem low. Remember, you're going to deal w/customers who'll come back and ask you to redo work because they are not satisfied for one reason or another, whether justifiable or not. You'll encounter old bikes with junk parts that will require far more than $5.00 of your time to adjust one brake, much less both of them.
You might do flat-repair as a loss-leader, but are you replacing the tube at that price, or patching it? If you patch it, someone will come back to you later with their tire flat again and blaming your patch job. If you replace, then charge enough extra to cover the cost of the tube.
I agree about getting insurance. Protect yourself. You are worth that much.
What's your basic value proposition? Are you less expensive than the local bike shops? Are you more convenient? Will you get work done more quickly? Given that you're in class most of the day, will it be easier for your prospective customers to just go to a shop that is open than to try and track you down? What is going to be your drawing card?
And charge more.
