"Be sober-minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour." (1 Peter 5:8)
Satan is father of lies (John 8:44). He enjoys nothing more than messing with our minds by telling us we don't deserve God's love and reminding us of our past mistakes. Don't believe it for one second! "Submit yourselves therefore to God. Resist the devil, and he will flee from you." (James 4:7)
Tell the enemy to hit the road and guard your heart:
"Above all else, guard your heart, for everything you do flows from it." (Proverbs 4:23)
"And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus." (Philippians 4:7)
"Then Christ will make his home in your hearts as you trust in him. Your roots will grow down into God's love and keep you strong." (Ephesians 3:17)
With Jesus in your heart, they'll be no room for satan's lies in your mind.