It is very possible. Even though your income went up, other credits you receive could have gone up more than the amount of tax you owe on the additional income. Also, it could be that the amount of withholding in Box 2 was more than enough to cover the tax on the increased income.
Also, the TurboTax home screen will always show the amounts from your original return, even 5 years from now. When you finish the amendment process, the resulting 1040X will only show the effects of adding the W-2 (net changes). Sometimes adding a W-2 creates an additional refund and sometimes it does the opposite and causes you to pay additional tax. If it had created an amount due from you, you would need to pay it by 04/17/18. However, since it created an additional refund, the IRS will issue you a 2nd refund after the 1040X is processed (usually about 14 weeks).
