First, you should fix the W4 with your employer right away to eliminate this problem for the 2018 tax return. Reduce the number of exemptions.
Next, a penalty could apply, it depends on the amount of tax due and/or when it is paid. The most important thing for you right now is to make sure you file the return on time to avoid late filing penalties.
If you tax due is below $1,000, there will not be a penalty if it is paid by the due date of your tax return (April 17th, 2018). Remember you can use a credit card for payment of your tax bill.
Making payment, or payment arrangements (wait until closer to the end of filing season) and filing your return will fix it.
For more details you can see the TurboTax article below.
https://ttlc.intuit.com/replies/4159821
