Do I always doubt that God will not accept my repentance or my prayers?

This feeling is dispelled by having a good opinion of Allah and recalling His mercy and favor, and by knowing that He is more merciful to His servant than a mother is to her child, and that He is as His servant thinks of Him. So be sure to have a good opinion of your Lord, and know that He forgives sins and nothing is beyond Him. Strive to rectify your repentance, be sincere in your supplication, and take the means to have your prayers answered. Be hopeful that He will answer your prayers and accept your repentance.