In First Corinthians, St. Paul says the Cephas (Peter) was the first that Christ appeared to after he was raised to life, yet in the Gospels it is said that Mary of Magdala was the first. I am confused.
Technically, the guards at the tomb were the first to see the risen Christ.
And for fear of him the keepers did shake, and became as dead men. Mat 28:4
Then Mary Magdalene and the other women saw Him. Then Cephas and the others saw Him.
Mary Magdalene came and told the disciples that she had seen the Lord, and that he had spoken these things unto her. John 20:18
In 1 Cor 15:5, Paul doesn't use the word "first", but simply that Peter saw Him and then the twelve.
And that he was seen of Cephas, then of the twelve: 1 Cor. 15:5
In First Corinthians, St. Paul says the Cephas (Peter) was the first that Christ appeared to after he was raised to life
This is technically false. Paul says that Christ "appeared to Cephas and then to the Twelve," but doesn't claim that Cephas was the "first" He appeared to. As long as Christ appeared to Cephas some time before He appeared to the Twelve, there is no contradiction.
(1 Corinthians 15:3-6) For what I received I passed on to you as of first importance : that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Cephas, and then to the Twelve. After that, he appeared to more than five hundred of the brothers and sisters at the same time, most of whom are still living, though some have fallen asleep.
Appealing to the Gospels, it is almost certain that Mary Magdalene was the first person whom Jesus appeared to. Perhaps the most compelling evidence is from Mark, which states "he appeared first to Mary Magdalene." However, some scholars have suggested that "first" might indicate nothing more than relative first among the mentioned apparitions, and not absolute first among every apparition ever.
(Mark 16:9-14) When Jesus rose early on the first day of the week, he appeared first to Mary Magdalene,out of whom he had driven seven demons. She went and told those who had been with him and who were mourning and weeping. When they heard that Jesus was alive and that she had seen him, they did not believe it.
Afterward Jesus appeared in a different form to two of them while they were walking in the country. These returned and reported it to the rest; but they did not believe them either.
Later Jesus appeared to the Eleven as they were eating; he rebuked them for their lack of faith and their stubborn refusal to believe those who had seen him after he had risen.
Thus, we can't be 100% sure that Mary Magdalene was absolutely the first person, but she seems to be the most likely candidate.
Others have instead affirmed that the Blessed Virgin Mary was the first person to see the Risen Christ, notwithstanding the fact that it isn't mentioned in the Bible. (Of course, just because an event isn't mentioned in the Bible doesn't mean it didn't happen.) This article does a pretty good job in summarizing the pros and cons of the theory.