If your grade in the CBSE Boards exam for grade 12 was 69%. You should take the admission exam for your UG programme rather than taking the 12th standard again in order to improve your marks. Because retaking the 12th grade would cost you a full year. It was a dangerous and demanding job to undertake because in NIOS you have to prepare themes for both classes 11 and 12. However, if you prepare for the entrance exam there is still hope for you to enter a good college and have a skillful and happy life if you wish to attend IIT or NIT. Don't worry, you still have the opportunity to visit and participate in them. When you have finished your bachelor's degree, you can apply there for a master's degree or post-graduation courses.

Just believe in yourself,

All the very Best.