Really any time you have blood in your stools you should talk to a doctor. I doubt you could wipe hard enough to cause bleeding. That would be pretty dang hard.
Does it hurt when you go? Hemmroids are possibly the culprit. Even if it doesn't hurt you can still have internal hemmroids. Do you strain to go or are constipated? This can also cause hemmroids. They can also be hereditary.
I'm sure there is a campus doctor you can talk to about this. Sure it's embarassing but really it's better to find out than be wondering. If it's simply hemmroids, it will ease your mind and give you some ideas how to prevent them from getting to the bleeding stage.
You need to keep your stools soft. Drink lots of water. Try not to strain. Eat more fruit.
Speak with a doctor please. Don't worry about cancer, you're far too young but crohn's disease is a bowel condition that younger people often get and would need treatment. Good luck to you.