Hi,
You can modify it if it gives you an option later. Before going for further steps it might ask you to validate your details and there you can modify.
Also,  You haven't mentioned which form were you filling.
Kindly post questions with more details.
Hope the given solution helps, good luck to you!

Hello Aspirant
Dont worry for the mistake you have done. There is no problem without a solution in this world. Just try contacting the admin of your respective college to inform them and if not then take your self attested copies alongwith you during your counselling session. Hope you find this answer useful. All the best.

Please specify the name of the college you're enquiring for. If it as regarding the admission in DU then no need to worry you form wouldn't get cancelled you can give attested copies on the day of admission but do not fill another form with same details as this will lead to the cancellation of both the forms.