What can I expect to happen with a first offense shoplifting charge?

As you are aware a shoplifting lifting charge is a misdemeanor, thus making it a criminal offense.  Accordingly you should without have legal representation in this matter.  An experienced attorney might be able to get the charge dismissed on a technicality or at least possibly reduced.

You are a first-time offender which will be of help.  Accordingly you will be eligible for "diversion" (or your state's equivalent).  This is an alternative program whereby you plead guilty to the charge, receive a special probation, and upon successful completion of the probation the charge is withdrawn and the case dismissed.  Your record should be automatically cleared.

Note:  Typically diversion allowed only for a first offense, so if you again get into trouble it will not be available to you.  This is why if you get an attorney is important.  If they who can get the charge dismissed, you will be eligible for diversion in the future if you should ever need it.