Yes I want to go for 12th class again

You want to appear in class 12th board examination but not willing to give the improvement examination. This cannot happen if you want to appear in examination, it has to be given through improvement only. No education board has a system of this kind that let's you give the examination without the improvement.You have passed your class 12th that's very good go for your further studies score good grades in graduation. It's just a criteria which you have fulfilled.