At 7 weeks post-csect, some abdominal bulging is still pretty normal, but it is genuinely hard to self-check for diastasis recti, especially without knowing what a gap is supposed to feel like. The self-test you described is roughly the right idea, but the technique and what you are feeling for can be tricky to assess on your own. I think the most reliable way is to bring it up at your next appointment, whether with your gynae or a PD, and they can refer you to a physio who specialises in postnatal recovery if needed. It is better to get a proper assessment than to guess, especially since the right exercises really depend on whether diastasis recti is there or not.