Psalm 51 is a famous Psalm of David from when Nathan the prophet went to him, after he had gone in to Bathsheba.
Have mercy upon me, O God,
According to Your loving kindness;
According to the multitude of Your tender mercies,
Blot out my transgressions.
We are human; we sin. The Lord sayeth that all sins are equal in his eyes. Do not be ashamed nor afraid to repent to the Lord your sins.