A lot of schools were caught out lastvyear with the new GCSE papers.
It's generally accepted that candidates who are borderline 4/5 are better off doing foundation or they risk failing completely.
I'm working between 6-8 (depending on the topic) & will be doing Higher but lots of classmates are doing foundation.
However final entries arn't due for a while yet (my mocks are Jan) so if you pull your finger out & start working at a higher level between now & the new year you could argue for being allowed to enter the higher paper.