FRIDAY: Put to death
SATURDAY: Fought satan
SUNDAY: Risin!
So, Jesus was dead for three days, but he was crucified in the noon time, and after hanging on the cross for a while, his death was sped-up from a guard's spear. This would have placed Jesus' death in the late afternoon/early evening. Jesus' burial would have needed to take place BEFORE sundown, as Jewish law for observation of Sabbath dictates.
Let's say Jesus' time of death was 4pm. If he rose from the dead at 4pm on Sunday, that is only two days - which should place the true "Easter" on Monday, not Sunday.
Regardless of the actual time of death, as the christian calendar notes was on Good Friday, and the Christ returning from the realm of death after three days - Sunday cannot be the day of Easter. Maybe if Christ died on Thursday, then Sunday would be right.