hi,

see the eligibility criteria for CA foundation course is for 12th standard candidate is candidate must secure 10+2 Courses  with a minimum of 50 percent aggregate from a recognized institute and/or board. candidates from any stream like science, commerce or arts background may pursue this course.

since your 12th exam is not completed you can not start CA foundation program.  follow the below link to know more details,

https://www.icai.org/post.html?post_id=6533