CS Lewis wasn't Roman Catholic. Never became Roman Catholic. Made it clear in his letters that he thought that Roman Catholics believe in doctrines that go beyond Christian doctrice - for instance, he said in one letter that Roman Catholicism, or at least its practice in some place, raises Mary the Mother of Jesus to "co-redemtrix."
I never heard that in Sunday School or in Jesuit high school.
However, if he literally meant "at least in their practice in some places", I guess anything is possible.
At least in their practice, a certain small Protestant group seemed to be raising Tammy Faye Baker to "co-redemtrix" whenever I channel-surfed past their cable TV station several years ago.