re: Am I calculating my taxes right?

If you are using a vehicle exclusively for delivery driving, then you would probably benefit from using the actual vehicle expenses rather than the standard mileage rate. In addition to the $135 of gas expense (rounding is okay for tax purposes), you can deduct the costs of insurance, registration and inspections, maintenance and repairs, and allowed depreciation. The allowed depreciation alone might be enough to result in a loss from this business activity. This would reduce your gross income, and your tax liability.

You could claim some expense for a cell phone and/or GPS system if you use them in connection with your delivery driving. You could also purchase a fancy flashlight to assist you in finding addresses at night. Another expense you could claim is any insurance costs directly attributable to commercial use of your vehicle if you decide to use the standard mileage rate.

As a matter of limiting your liability, you should insist on being treated as an employee instead of an independent contractor. Unless you have absolute freedom to choose which deliveries you make and which deliveries you don't make, you are technically an employee instead of an independent contractor. If you persist working as as a non-employee, you might want to consider forming an LLC to limit your liability to the assets you use in the business, i.e. the delivery vehicle and any insurance coverage you have on the vehicle. The expenses associated with the LLC would also be allowable deductions for determining net income from the business.