I’ve done a pregnancy test today even though my period is due tomorrow because had no pms symptoms and that’s not usual at all.

I just need some advice because I’ve done the test, seen one line coming up and left thinking it was negative, came back after 20 min and the line was there!! Read the package and it’s says to read in 5 min, does the fact of reading it after

20 could be a false positive?? Thank you