Your disciplinary records are sealed and grad school's won't find out unless you tell them. The school can't officially tell you to lie to grad schools but then can say that they do not report minor offenses like this. It is a wink wink situation because it's between you and Cornell and no one else needs to know. This has been the policy for first time alcohol and marijuana offenses (unless if has changed very recently).

Do everything you are required to do and be gracious about it. Complete Basic and community service if you are required to.

It's awful that you're dealing with this your first week of freshman year. In the long run, it'll prevent you from making future mistakes that could actually hurt your chances of getting into grad school. I'm sure you have learned a lot from this experience. You should not have been smoking but let's face it, hundreds of kids did the same thing this weekend and didn't get caught. You were unlucky but you still made a mistake. Learn from it.

Do not get a second offense and everything will be fine. Try to stop worrying. In a month, this will all be the distant past to you. Enjoy the rest of your time at Cornell. It is a wonderful school and you will make lifetime friends. Four years go by in a flash, don't waste a minute being upset. Everyone makes mistakes.