Hello Aspirant

You don't have to worry about doing an extra section in your KVPY, there will be no major problem for you and so many students have done it in past as well.

Your final marks will be calculated on the best two sections which you did and your section with lowest marks will be neglected and will not be counted in your final marks , so if got lowest marks in section 3 your marks will be calculated according to your marks in section 1 and 2 and you will not loose marks based on it .

So it depend if your marks in section three are in top 2 or not , also please take care of these mistakes in future examination and read and understand the exam patter and instructions carefully

Hope this helps.