A few verses? That's objectionable.
I've explained that Peter in Acts 2 wanted to emphasize Jesus's life, death, and ressurection to the crowd. Peter simply didn't give this theological discussion, unlike the author of Hebrews. Sometimes different passages in scripture emphasize on different things, and all together they form a coherent and complete picture. That's probably my biggest argument.
Honestly, I don't see the passage from I Peter as a contradiction to the belief that Jesus was a preexistent being. He was a preexistent being and his purpose on earth was foreknown. The existence of Christ-related prophecies would immediately support that. So, why can't you accept both?