Luke 5:8 New English Translation

⁸But when Simon Peter saw it, he fell down at Jesus’ knees, saying, “Go away from me, Lord,^[a] for I am a sinful man!”^[b]

Luke 5:8 sn Lord is a term of high respect in this context. God’s presence in the work of Jesus makes Peter recognize his authority. This vocative is common in Luke (20 times), but does not yet have its full confessional force.
Luke 5:8 sn Peter was intimidated that someone who was obviously working with divine backing was in his presence (“Go away from me”). He feared his sinfulness might lead to judgment, but Jesus would show him otherwise.

New English Translation (NET)