Yes. if drug charge was dismissed, you are OK.
NYC EXPERIENCED IMMIGRATION ATTORNEYS www.myattorneyusa.com; email: email@example.com; Phone: (866) 456-8654; Fax: 212-964-0440; Cell: 212-202-0325. The information contained in this answer is provided for informational purposes only, and should not be construed as legal advice on any subject matter.
Since your case was dismissed based on lack of evidence to support the prosecution, and the U.S. Customs Officer let you in, your application should be granted. But you will need a lawyer, to make sure that USCIS was impressed upon that there can be no finding of drug possession.
It is impossible to say based upon a few sentences you post online. If you are serious about this you need to speak with and retain an immigration attorney to determine the best path forward for you. Do you really want to risk your legal status by trying to figure this out online on your own?
Legal disclaimer: The statement above is general in nature, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship.