Head teacher Richard Park said it didn't really show how good Peter's singing can be and it was "out of tune".
Carolynne was in tears as Peter waved goodbye.
Earlier in the show the pair had sung a duet and looked like they really enjoyed it.
On Saturday's show, she teamed up with Alistair to belt out Everybody's Talking.
The final three have just one week left before the nail-biting final.