Print out your return and see what line line the 802 is on. You must have misread it. Although it seems too early to get a tax due letter.
Did you enter an estimated payment on line 18d you didn't make? Or is line 17 for withholding too much?
How to get a copy after filing
https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-get-a-copy-of-a-return-i-filed-thi...
