That's why FIRSTFRUITS is the THIRD DAY following Passover.
The firstfruits was on the 16th of the month while passover was the 14th. Jesus is firstfruits of resurrection.
Leviticus 23:11 And he shall wave the sheaf before the LORD, to be accepted for you: on the morrow after the sabbath the priest shall wave it.
1 Corinthians 15:20 But now is Christ risen from the dead, and become the firstfruits of them that slept.