Read it again.

Jesus was telling Peter that the rock that was the cornerstone that the builders had rejected.

Now, who was rejected by the builders? Jesus was rejected by the leaders of the temples, not Peter.

SO, Jesus is the rock, that the church was to be built on, not Peter. We are to follow Jesus, NOT peter.

Peter was never rejected, this is very important and life changing for many who will read it and finally understand that Jesus is whom we need to follow, not Peter, not Apollos, not Paul.