It does not depend on whether you think that you have qualified the examination or not. When you go to register for the Joint Entrance Examination Advanced registration page, then they automatically ask for your JEE Main details and depending on that they tell you that whether you are eligible for JEE Advanced or not, thus answering your query. So, go to the JEE Advanced registration page and you'll be answered automatically.

You can also use our college predictor to see your chances in all the colleges:
https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Hope I have answered your question. All the best!