It is a hard thing to let go of mistakes we've made and sins. God wants us to do that because He knows the guilt and the condemnation will keep us from becoming who He has created us to be. Salvation and Christ's love is a gift. You don't earn it. You've got to receive that gift. I think one of the most important things is starting off the day forgiving others and forgiving yourself. You learn from your mistakes, but I don't think you have to drag them back into today.