Dear Anupama, 

As has already been stated, you do not need to necessarily submit your certificate of Class 12 right at the time of applying for CLAT, but will rather need to produce the certificate at the time of counselling or admission. The official CLAT brochure also states that those appearing in Class 12, they can also appear for the CLAT. The exact wording states: "Candidates who are appearing in the qualifying examination in March/April, 2019 are also eligible to appear in CLAT-2019 examination. However, they shall be required to produce evidence of their passing the qualifying examination at the time of admission, failing which they shall lose their right to be considered for admission."

Since you will appear for Class 12 boards in March 2019, you can worry free apply for CLAT 2019. 

Hope that clarifies. 

All the best!

As per the eligibility Class 12th pursuing students can apply for CLAT Entrance Exam, At the time of Counselling/ Admission, You will be required your 12th marksheet & other documents. You can check teh complete information with teh given below link.

https://law.careers360.com/articles/clat-eligibility-criteria

Good Luck!