Hello

I assume you had a total of 5 subjects including 1 English, so you can choose domain subjects from the other 4 subjects, and you can choose your additional subject as the domain subject also there is no problem in doing so.
Keep a check that you don't select the wrong domain as this will hamper your admissions.

Senior's advice: Select as many domains as you can as this will help you in maximizing your score. Do not restrict yourself to only 3 domains.