You have three attempts at each question in the case study. There is an overall pass rate of 60% across all of the case study modules so if you do fall below 60% in one area you can make up for it in another. The case study isn't designed to catch you out and you will receive prompts and suggestions and be able to link back to the relevant parts of the course to refresh your learning.
If you don't achieve the 60% average you would still have access to the course but you would not receive the certificate. We do think that 3 attempts will be plenty for most candidates though.