Your rank list is water under the bridge. Now you need to focus on becoming a great general pediatrician and start exploring subspecialties that might interest you. You will see less cystic fibrosis if your program isn't affiliated with a CF center, but you will see plenty of asthma, BPD, chronic respiratory failure, recurrent pneumonia, etc. You need to confirm that you can at least tolerate taking care of those issues if you want to be a pulmonologist. There also may be some CF patients who are seen at your program anyway.
So how can you get CF experience? First, is there an adult CF center affiliated with your hospital, medical center, etc.? That may be the first place to look. You might also be able to do electives outside of your program where you can rotate through an outside hospital's CF center clinic or on the inpatient pulmonology service where CF patients are admitted. There is a significant difference between the types of CF patients you see in clinic vs. the ones admitted to the hospital in terms of management and overall health, so both experiences would be beneficial. Some centers have certain days of the week where they see all their CF patients, so spending a few days there would give you a lot of bang for your buck in terms of seeing the general approach (physicians, nurses/coordinators, respiratory therapists, social workers, and nutritionists).
I would also recommend getting involved with some type of pulmonology-related scholarly activity. This could be research or a quality improvement initiative. That would further showcase your interest and dedication to the field.
Finally, the CF Foundation offers a Resident Roundtable Travel Grant to the annual North American Cystic Fibrosis Conference that pays for your travel to the conference and gives you the chance to meet with CF docs and researchers. This is a great experience and one that you could consider pursuing (likely as a PGY-2).
As you mentioned, pediatric pulmonology is not a competitive subspecialty in terms of the match. If you are successful in residency and do some of the things above to show your interest, I have no doubt that you will match somewhere.
