Mark,
UC can cause thin stools too because of the improper contractions of the colon. I'm certain you see a gastro who dx your UC. Next time you see him/her, hopefully within a month or so, mention it to them and ask for another colonoscopy to make sure you don't have other issues going on. I don't know when your last scope was??? But follow up with your gastro.
I had narrow stools, turned out to be severe constipation.. i increased my fiber, excersise, and take a stool softener, everything has turned back to normal...