On your tax return there is only one bottom line. Either a refund or Tax due. It is for all your income combined. If you have a tax due on line 37;you don't have a refund.
Your W2 withholding wasn't enough to cover the tax on all your income plus the self employment tax on your 1099. How much self employment tax do you have on line 23 and Schedule 2?
You pay Self Employment tax (Scheduled SE) on a Net Profit of $400 or more on Schedule C. You pay 15.3% SE tax on 92.35% of your Net Profit (If it is greater than $400). The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare. So you get social security credit for it when you retire.
The SE tax will be included in your tax due or reduce your refund. It is on the 1040 Schedule 2 line 4 which goes to 1040 line 23. The SE tax is in addition to your regular income tax on the net profit.
