I don't think you did anything wrong. There are two ranges in my area. The first seems to have every first-timer and "Imma take a buds out a go shootin" person in the state. It's always busy, and you can see a few people being a little reckless. That's why it has video cameras that are constantly monitored, with a PA system that the range owners can use to call people out if their doing something wrong. It has about 20 lanes.
The second is much smaller. Maybe 10 lanes. It's frequented by off-duty LEO and other people who seem to be more serious. I usually go to this one.
At both of these places, it's very common to hear shotguns go off. I stood next to a guy shooting his .44 mag just last week. I shoot slugs and 3 inch mag 00 buck. At one of the ranges, only slugs and 00 is allowed to be shot. At the other, it's not uncommon to hear people with Class IIIs going full auto.
If people have a problem with noise, they shouldn't be at a gun range. Guns make noise, and frankly, if you're ever forced to use your gun to defend yourself, you most likely won't have the option of throwing on some muffs. And in a gun fight, there will be some big booms. Getting over the instinctual flinch is important.
For outdoor ranges, maybe you can get away with some cheap plugs, but if you're shooting indoors, you better have some good muffs.