As a parent, all I want in life is for my son to be happy. What money I have exists to support that goal; there is no better use for it. So, if your parents are comfortable paying, no need for guilt.
What you can do for them, as well as for you, is to thrive. Do well at college. Enjoy it. Make good, thoughtful choices. Grow into a happy, confident person who will be a source of pride and joy for your parents.