How to find exact location of my lost iPhone
There is no app to do what you want. The accuracy of the GPS used by "find my phone" is not good enough to tell you where the phone is with the accuracy you desire. I would go back to the store and tell management what you are doing and then try calling your cell phone number. Maybe the phone's ringing volume is loud enough to hear. If you don't have access to another cell phone maybe you can use the store's phone to call.