Something doesn't seem right. I entered a W2 and it said I'd get a refund of $115. Then entered my 1099-MISC, for which I'd owe $499, but balance due became $1200+!

It depends on how much your 1099-MISC was for. If your 1099-MISC showed income in box 7, it's subject to not only income tax but self-employment tax, which is the equivalent of the FICA that gets withheld from your wages.

For 2017, the Self Employment Tax rate was 12.4% for Social Security and 2.9% for Medicare. You can claim 50% of what you pay in self-employment tax as an income tax deduction, which TurboTax computes automatically. 

See this for more information on Self Employment Tax.

Thank you, this really helped me understand what I was facing. I’m just a little shocked, as it’s my first time doing this side gig, and now 38% of what I earned isn’t mine. :(

I understand that completely!