Let me give you some general advice. Confession is for your benefit, not the priest and not for God. When you confess something sacramentally, you are recognizing that you have fallen from Grace through sin and you are expressing the desire to be reconciled to God. This means that you are truly repentent, desire to sin no more and that you expect to make reperations for the harm you have done to your relationship with God.
Having said that, if your conscience is telling you to come clean with the details, it is doing that for a reason: most likely because you need to come fully to grips with what you have done to move forward. Don’t worry about the priest judging you, he won’t. He’s an instrument of Christ’s mercy and he will be very supportive if you are truly contrite. However, if he senses that you are lying to him, he does have the option of withholding absolution, because absolution is only for the truly pennetent…