Assuming you have now been charged with a crime (you don't expressly say so), then you need to consult directly with an attorney for him/her to assess your circumstances, and to then advise, defend, and advocate for you. Sounds, based on the limited info you present, you have a good defense but your attorney will have to review everything before firmly reaching that conclusion.
Disregard the warning if necessary. The store has the ability to ask any patron to exit the premises. A failure to exit the premises could result in trespassing charges. If you go to the store again, and they ask you to leave, you should leave. Otherwise, you do not have to comply with a security guard's warning not to return for a false accusation.
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Report the false accusation against you to the corporate home office of the store. Their shareholders might like to know that the help is falsely accusing customers of stealing.
NONE OF THE INFORMATION PROVIDED HERE IS MEANT AS, NOR INTENDED AS LEGAL ADVICE. THE LAW IS CONSTANTLY CHANGING AND INFORMATION DISCUSSED IN THIS BLOG CAN BECOME OUT-DATED WITH THE PASSAGE OF TIME.