While you cannot fail the PiCAT, you can fail the first section if you do not get the right score. This is set by each branch and ranges from 31 - 65. Aside from the first section, your score on the assessment will guide the military recruiters as to whether you have the right vocational aptitude to be successful in your chosen role.
If you want to retake the PiCAT unless there are extenuating circumstances you have to wait for two years.