Is it uncommon for crohn's to turn into cancer?

Low: Before it was possible to treat crohn's effectively, around 2% of patients eventually got a cancer in or near an affected area; since this was often the small intestine where cancer is ordinarily very rare, it's reasonable that the turnover of the epithelium in active crohn's promoted it. Today it is almost certainly less. It's a difficult disease; good luck.

Yes: Yes, it is uncommon. Patients with ulcerative colitis seem to be at higher risk of developing colon cancer than those with Crohn's disease. But if you have extensive longstanding Crohn's disease of the colon, you should still have surveillance colonoscopies every few years.