When you appeared at the boarder it is up to the immigration officials to determine if you are eligable to enter the United States. In other words, are you admissable. Section 2129a)(2) of the Immigration Act gives one of the basis for inadmissability grounds is a conviction of a "crime involving moral turpitude." In most cases, shoplifting it itself is not determined to be a crimes of moral turpitude under the immigration law. You should contact an immigration attorney who can assist you as although you have not been adjudicated convicted for purpsoes of criminal law but may still be been adjudicated guilty for purpsoes of immigration law. Good luck
Legal disclaimer: The statement above is provided by CC Abbott is based on general assistance and not intended to be a legal opinion because not all the facts are provided. The person requesting information and all others reading the answer should retain an attorney who is permitted by the state bar within the jurisdiction who can examine the complete facts and provide a legal opinion on your case. All information provided in the above answer and other information provided by CC Abbott does not create an attorney/client relationship within any state of Federal law.
Because you have not been "convicted" for immigration purposes you should not have a problem trying to reenter with your B1 visa. Keep in mind, however, that you may have problems trying to renew your B1 visa in the future.
As far as expungements or sealing the record, it will not matter.
As previous attorney pointed out, it is smart to have an experienced immigration attorney on your side.