Common App-Interested Majors

Many schools ask the question about which majors or areas of study I am interested in.
For example, it states: “What academic disciplines interest you?”

How set in stone do our answers need to be? If I have slight doubts, should I just put in “undecided” or put in the major I am considering?

If I wrote my common app essay about my passion for writing, should I only put in writing? Will writing down a different major I’m considering negatively affect my application? I’m looking to double major.

It also asks for three areas of study, and I currently have only two serious choices in mind. Should I just put in a third choice that I am interested in or leave it blank?

Thank you for any comments or input!