2 things would have happened here. Either you entered your Category as ST Category and hence that amount was considered as the application fees or secondly you must have entered the wrong amount. If you entered the wrong Category, you cannot change your Category in the application form and hence you may have to re-register with a new email id, mobile no#, fill in a new application again and make a payment again for the correct amount. Now, if you entered the wrong amount manually, the application will be rejected for making insufficient payment and in this case again you will have to re-register.