I will go over what will be happening if you fail your US Citizenship Interview at the first time.
If an applicant fails any portion of the English test, the civics test, or all tests during the initial naturalization interview, USCIS reschedules the applicant to appear for a second examination between 60 and 90 days after the initial examination.
If you fail the second interview, your citizenship application will be denied and you will have to reapply after studying and preparing some more.