ezjmim and chowder are right. Basically if your a fuck up you'll do bad whether or not you smoke. If your a good student you'll do good whether or not you smoke. I was a fuck up in high school, got stoned all the time, and barely graduated with a 1.something GPA. I screwed around for a few years but finally got my shit together and went back to school. Even though I kept smoking I still ended up getting my BS and graduating with honors.

Since you already have a scholarship I'm guessing you aren't a fuck up. So just remember to set your priorities. School comes first so don't smoke when your at school, don't smoke when your studying, don't put off researching a paper so you can get stoned etc. etc. You'll do fine.