Replying to Stupid accident, stupid me

So I know this is NSG and the likelihood of getting a straight answer is low but I figure what the hell why not share my stupidity. Two years ago there was a massive accident going over the pass. I think it ended up being 8 cars all in the left hand lane of a two lane highway with high traffic in a shit storm of rain. I had distance in front of me and behind me and when the asshat in the very front decided to slam on his brakes, 3 cars rear ended each other in front of me. I slow down and stop to avoid rear ending the guy in front who has now stopped as well. Behind me the subi stops and doesn't hit me. We were all going about 40. Then shit gets real. In my rear view mirror I see what I can only be described as armageddon. Cars begin to plow into each other and then hit the subaru. A truck drives into the guardrail, a car goes into the ditch, a tornado looks to be forming and a train seems to have derailed near by. The last two aren't true but as I sit in my bubble of safety, untouched by those in front and behind, all I hear is my asshole whistling from the pucker factor.
When it was all done I pull off to the side. I had not hit anyone, nor got hit. I hop out to check everyone else out and then make sure people are ok since I have some basic first aid. No one was injured thank God. Since I didn't get hit and I'm pissed that its pouring and that my drive is now going to be significantly longer I opt to do what any stupid person would do; leave. Two hours later I get a phone call from the highway patrol asking why I had left the scene of an accident. I explained that I did not hit anyone and no one hit me so after checking everyone I felt I could leave. I did realize my mistake at this point and apologized and asked if I could turn around and drive back to help the cop out with witness statements etc and try to be as cooperative as possible. After all, he almost put me down as hit and run but was relatively understanding and just got my witness testament over the phone.

Now my questions. I clearly need to go to a few classes on the law. I should have stayed but is this a crime to leave even though I didn't hit anyone? I'm a witness I do realize I should have stayed and am an idiot for not doing so. People on the freeway who get in two car fender benders who watched them crash don't always stop to help. I see it this way.

Second, I got a claim from the other persons insurance stating I was involved and did cause damage to other cars. This is not true, but then again I'm not at fault. Since I wasn't there with the cop to prove I had no damage and the people in front and behind had no damage, my word isn't going to hold up to remove this from my record completely. I've heard anywhere from 3-7 years. This hasn't affected my rates as of yet thankfully, but I'm sure if i change carriers it sure would get brought up.

TL;DR I'm an idiot and left the scene of an accident even though I wasn't hit and only a witness. Am I at fault and how long is this typically on record. Learn from my idiocy and don't leave even if you didn't cause damage!