As a former employee for the competition, both stores have issues hiring people who don’t know enough and get fed questionable info from the training info. They may have been confused between superworms and mealworms depending on size of the turtle maybe? Even then if it’s just a treat a couple times a week that shouldn’t be an issue. Maybe if the only meal was supers? Shrug
I see the mention of the basking spot and heat lamp. Don’t forget the UV light. Also, super handy calcium supplement… Bird cuttle bone. It’s cheaper than the ones marketed for turtles. Just get the bird one, break it into halves and let your turtle have fun.
For the wounds, make sure the water stays clean. Unless the wounds begin to look seriously infected, that will go really far for the healing process. If the wounds do look worse or his belly also starts to look red, he might need a trip to the vet for a course of antibiotics.
The shell could be a combination of poor water quality for the store tanks and not enough vitamins/UV. Hopefully it will improve in time. If the areas between start looking white and fuzzy, that would be a shell rot issue.
Hope the little one heals up well for you!