Is your dog struggling specifically with training inside stores, try working on your skills outside the store first:
Only progress to training inside (that might be in a different session) when you’re 100% happy with your dog’s behavior outside.
Here’s a case study I wrote a while ago about a client’s dog with whom I did this exact progression:
https://spiritdogtraining.com/staircase-of-excitement-or-getting-kicked-out-of-petsmart/