If I only earned social security, do I have to add my mortgage info?

No  If your only income is social security, you have no taxable income.  No need to enter deductions.  If you want to clear your return, Click here for the steps to Clear your return and start over.

If you only get ssi or SS or SSDI  it is not taxable and you do not have to file a return.  And there is no benefit in claiming dependents or deductions.   Unless you have federal income taxes withheld from the benefits or you get health care insurance through one of the state marketplace exchanges and receive a Form 1095-A then you need to file a tax return.