All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
This action is extremely prohibited; rather, it is an act of Kufr (disbelief) – may Allah protect us from that. Whoever willfully proclaims himself to be a disbeliever without what constitutes coercion according to the Sharee‘ah, has committed an act of disbelief. If you repented sincerely to Allah, The Almighty, and performed the prayer, which clearly includes reciting the Shahaadah (the two testimonies of faith), then you have done what is required of you to do.
You should beware of Satan in the future, and know that whoever turns to Allah, The Exalted, with sincere repentance, it wipes out all traces of his sin. Verily, the one who repents of a sin is like the one who did not commit that sin at all.
Allah Knows best.