Agreeing with the others, be happy you matched.
It's ok to have a bit of a grieving process though. I was fortunate and matched on the other end of my list, but I too kept thinking about the what ifs and other programs I also liked. No matter how good you are, you can only match at one program.
You're clearly a very solid student and will probably be a fine resident. When you are doing interviews next year, you'll see how much it's really all about fit at that point and ranking highly the people you think best fit in with your program. You'll see everyone's applications and first wonder how you ever matched at all and secondly have no idea how you're going to distinguish these people. Everyone has numbers like yours, and they all have other amazing things that are vastly different yet all equally amazing. I mean how do you decide what's more impressive between 30 people with numbers like yours and CVs full of things like combat fighter pilot, Olympic athlete, professional athlete, founders of successful start ups, professional musicians and artists, stellar work histories at big name I-Banks and consulting firms, and the list goes on!
18 programs is a lot though and while it may be that you were just outside match range at most of those above you, you may want to consider the possibility that you are coming across poorly in interviews. It could also have been some other red flag on your application, maybe a meh LOR - hard to say. The only 2 reasons I've seen for applicants with stellar stats to match poorly or not at all are interview skills and/or a red flag on the application.
But in the end you matched, you're going to have a chance to become the kind of surgeon you want to become, and that's a pretty awesome thing. Matching a surgical sub is no joke and is a particularly grueling process that few people can truly understand.