Completed tax return but have not submitted--realized I did not report health care responsibility.

If you have not FULLY Submitted, you would still be able to add in the information before you submit your e-file, So no need to make an amended form-as that's only done after you submit and the IRS received and accepted your return.

 At this point you can navigate to the FEDERAL section and go to the Healthcare portion to add in the information you need prior to e-filing..  Hope this helps..