Hi,
Sports for people with CF are good. Anything using your arms is great as it stretches and excercises your lungs. Cross-trainers at the gym are fantastic as you're doing cardiovascular work along with arm movement. Start off slow and work up. There are people with CF who are doctors, surgeons, body builders, wrestlers. You shouldn't let it stop you.
Obviously be sensible, if you start suffering severe breathlessness, pain in chest or coughing. Stop for a bit, then start slower next time. Excercise is the number 1 best treatment for CF lungs.
If you're still unsure, ask a physio, as they'll be able to get your medical records and advise you better. But, as a general rule, lots of activity and excercise in CF makes for a healthier body and mind too.
Also, playing a musical instrument, something like the trumpet. It's hard going to start with, but I still maintain that playing a trumpet growing up, is the reason I have such good lung function at 26.
Hope this helps.
Gemma :)