No one can ever be so bad or so sinful that God will refuse to forgive him or her -- not if they are sincerely sorry for their sins and repent of them, and truly trust Jesus Christ as their Savior and Lord.
Think, for example, of the Apostle Peter, one of Jesus' closest disciples. After Jesus' arrest, Peter denied that he even knew Him -- not once, but three times -- and yet God forgave Peter when he repented and sought Christ's forgiveness. Peter went on to become a great leader in the early church.
On the other hand, Judas -- another of Jesus' 12 disciples -- was not forgiven for what he did. You'll remember that he betrayed Jesus by going to His enemies and promising to reveal where Jesus could be secretly seized by them. They paid 30 pieces of silver for his information, and Judas carried through on his promise -- resulting in Jesus' arrest and death. Later, Judas bitterly regretted what he had done -- but he never repented or turned to God, and he died unforgiven and lost.
I can't help but wonder, however, why you've asked this question. Are you afraid your sins are so great that God will never forgive you? If so, I have good news for you! God loves you, and Jesus Christ gave His life for you. Don't stay away from Him any longer, but open your heart and life to Him today. God's promise is for you: "If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness" (1 John 1:9).