The official count is from the First Sunday of Lent (day #1) to sunset on Holy Thursday (day #40). Somewhere in the Middle Ages, it was found that if you subtract the Sundays, stretch it to Ash Wednesday and Holy Saturday on the ends you get forty days of penitence. So how is Lent counted?
Liturgically, the season includes Sundays and excludes the Triduum.
Spiritually, your days of penitence number forty including the “Ash Week prelude” and Good Friday/Holy Saturday.
If you’ve already screwed up on a Lenten resolution or two, become a liturgist. Tell yourself everything this week is “Spring Training” for Opening Day on the 5th … and threaten to send yourself to the minors if it happens again.