Babies head are moldable and flexible. Your cervix will dialte to 10cm and you will birth your baby. When you are in labour you are not gooing to be able to tell the difference of afew cm when you are pushing your baby out, it will still hurt. I had some minor tearing when I birthed DS1 who was 6 weeks prem, DS2 who was term slipped out, no tearing.
I'm sure you will be just fine, good luck.