I forgot to report a W2 ...?

I Forgot to add a W2 to my taxes this year.. Between BOTH W2s I made roughly 24,000 for 2013. On the W2 I forgot, I made $7,000 Wages and 754 in Federal.. IRS told me they may fix this issue before sending my income tax return to me. But if they don't correct it, I need to file an Amend Form (1040x) I understand this completely.. What i am NOT understanding is, How do I know if I need to pay the IRS money for that W2 or If they need to pay me. I have 1 dependant, Claimed Head of House hold.. Can someone PLEASE help me with this, so I know how much money I need to pay before April 15.