Hello,

There is nothing to do now. If you have submitted then it is gone. Even it is a mistake you can't change it in anyway if it is once done. If you want then you can mail to the help desk and ask for help or any guidance if anything can be done but you can't change anything now.

In the exam hall there are invigilators who take care of all this stuffs still you made a mistake then it can't be helped out.