Assuming I found the correct calculator, I ran the numbers you provided and also got a result of more than $200 per month .. $2584 to be exact. Upon inspecting the results (click the "Detailed Results" button), what stands out is the "Self-employment tax" of $2515.
Because you entered Self Employment income and not W-2 income, you're triggering the self-employment tax, which is designed to capture contributions to Social Security and Medicare. There is no employer making such payroll deductions and contributions on your behalf.
If you had W-2 income instead you, personally, would have paid half of the Social Security tax due and half of the Medicare tax due through payroll deductions, and your employer would pay the other half. In this W-2 context, the same contributions are commonly known as FICA taxes. Once you are self-employed, you end up paying both what you would have paid as an employee, and what the employer would have paid .. and they call the taxes self-employment taxes. But they're still just Social Security and Medicare taxes.
Also, the deduction for student interest would be limited to $2500 per year.
I would suggest the results you received are reasonable.