Yeah...there's not always fire where there's smoke...ha.As for your "innocence"... Have you heard the adage "where there's smoke, there's fire"? I suspect it applies in your situation.
I'm not sure you can give very good advice here if all you're going to do is assume guilt.
Why would I buy/carry pot on campus when they already think I have it? That wouldn't be very smart, would it. I'm not trying to get kicked out of school.