I repented, but then I regretted it. What should I do?

Repentance is among the rituals of God and His obligations that He commanded His servants, and insulting it is an act of disbelief. Whoever insults it must offer sincere repentance to Allah Almighty, abandon this sin, resolve not to repeat it, and feel profound remorse for having committed it. The two declarations of faith must be uttered. As for ghusl (ritual bath), it is not obligatory for an apostate unless they committed something during their apostasy that would necessitate ghusl.