Ankita, truth be told, this is an error that shouldn't have happened. The reason why you are asked to enter your 10th and 12th marks are to check your genuineness of you passing the respective Boards and being eligible for NEET. Now that the correction window has been closed, you cannot make any changes right now. You will get the admit card and you can appear for the exam. When you have to fill in the online registration form, please fill in the correct Board marks. And during document verification, as you will also take along with you  your original marks sheets and documents, it should be fine.