That's too much still. For each bin, say 1 inch of bedding in a 10 by 10 space, put no more than 1/4 of a potato or about 3 inches of a carrot. I've learned this the hard way...less is more with mealworms. If the humidity is too high, even just a little too high, you'll end of growing mold or create a breeding ground for book mites.
About PetCo's mealworms...I have that problem with my local store too. They are understaffed and no one checks the mealworm/waxworm/superworm stock. When I buy them, I always check the containers before I leave the store...sometimes openning every one to find the one I like best.
The good news is, you can take that back to the store and they will exchange it. They have a wonderful return policy and will take anything back...even a half eaten back of dog food because your dog didn't like it. 