Question

Checked wrong box

I checked the filing single box when in fact i am married. What do i do

You can include your spouse in your personal info, using these steps:

Click My Info (in the black bar on the left of your screen).
Click on Edit next to your filing status.
On the next screen, Let's confirm your marital status, mark the radio button next to Married.
Under the question, Do you want to file this return together with your spouse, mark Yes and click Continue.
On the next screen, enter Your spouse's personal info.