I usually hang out on the UC forum but I saw your post and thought I'd answer. I do not believe there's blood involved with IBS. Now, I don't know how old you are but you are more likely to have an IBD (inflammatory bowel disease) than cancer if you are younger. Not that cancer isn't possible of course but less likely.
Usually, if you have blood in your stool you will have further testing...lab work, stool samples, scope...to determine where the blood is coming from.
Don't freak out, just find out what the cause is and go from there.
Hope you find some answers.