OP, I would say that you committed a very minor social error, which you realized yourself. Now you know that if you have to go to another viewing, it's better not to wear jeans. That being said, though, I suspect that the family won't have thought twice about it.
For what it's worth, my MIL and FIL arrived for my mother's funeral slightly late and wearing everyday clothes. I didn't mind in the least, because I knew they had driven four straight hours to get there, and were going to drive four hours back again that evening. It was just so good to see them there.