I also don't know questionnaires but your idea sounds reasonable. So you want to use the feedback interview to assess the DV of your experiment, is this correct? What are your probing questions in the interview? I think it should be possible.
Thank you so much for responding! So my topic is 'Role of self-affirmation on relationship between attitude towards Facebook and its usage'. Basically I want to find out why are people on Facebook despite an unfavourable attitude towards it. To measure attitude towards Facebook, I have constructed a scale and the experiment is based on the assumption that positive feedback on Facebook posts will lead to affirmation. So the feedback interview will more likely be an introspective report asking the participants about Facebook usage and questions like- How did you feel about the likes and comments you received? What kind of responses did you get? so on..