I do hope that you won't judge the US by your experience in Denver. That is absolutely horrible and I am so sorry. All of us here don't carry around guns and the like in this country. We do feel safe living in our towns and cities despite incidents like this and the news that make it sound like violence is happening all of the time.
I am hoping that you heal quickly. You don't want to miss too much school. It's too hard to get back when you take breaks wanted or like this one unwanted.
BTW,my daughter lives in Denver and you have given me another worry.....She hasn't had any problems there and I hope it stays that way!