Thank you, but I thought that physics and chemistry can only be done if you chose math in 11th and 12th. Is this true?

If you have made mistakes in the application form, but have not submitted the application form, then you can change the particulars entered any number of times in the application form by using the edit option. However, the details entered for registration can not be changed. If the application form has been submitted, then you can not edit or change anything in the application form. In such a case, you have to fill a fresh application form using a different email ID.