I disagree.

I think you should call the department or agency to which you are applying and speak to your background investigator prior to your CVSA.  Tell them about your omission and don't try to conceal it.

If the sum total of your illicit drug-using experiences is eating a marijuana brownie while in college, that is not a disqualifier for any law enforcement agency with which I am familiar.  However, lying about it will likely DQ from most, if not all, agencies.