If you entered the mortgage interest, and if it made a tax liability difference, it would be listed on your Schedule A line 8 and carried over to your 1040 line 8.
If you took the Standard Deduction INSTEAD OF the Itemized Deduction, THAT amount would be on line 8 instead.
If the standard deduction was selected (it is much higher for tax year 2018) you won't know if you entered it into the system without going back into your account and looking at the entries (under FEDERAL; DEDUCTIONS & CREDITS; YOUR HOME.
The ability to amend a return won't be available until next month. You should wait until the original return has processed before filing a 1040X.
Below is a link for the form and instructions to the Schedule A. It may help you determine if entering the mortgage interest would matter.
Also below is a link for amending a return.
https://ttlc.intuit.com/replies/3288565
https://www.irs.gov/pub/irs-pdf/f1040sa.pdf
https://www.irs.gov/pub/irs-pdf/i1040sca.pdf
