The police have one primary interest in talking to you - to try to get additional information from you which would justify charging you with shoplifting. If you feel you must talk to the police, talk to a criminal defense lawyer first.
If you don't wish to consult a criminal defense lawyer, consider notifying the police by telephone that (a) the incident was a misunderstanding, resulting from your going out to your car so you could complete your intended purchases, and (b) you are sorry for the misunderstanding. If they say that's not good enough, or they press you for more details or to come in for a meeting anyway, apologize and indicate that you will have to consult a lawyer before you can answer any further questions.
They want to see you in person so they can try to break you down and get you to confess to shoplifting. You don't have to go along with that game.

