Help with air travel!!?

So my sister and I are going to go in on a ticket to alaska for late July, we plan on buying the ticket in about 3-4 days. I am 15 and the ticket price as of now is $638. What I'm wondering is if I will have to be accompanied by a chaperon on the plane. My flight would be nonstop from Minneapolis/St. Paul, MN to Anchorage, AK. Although it is my first time flying I think I can handle it without somebody looking after me considering it is nonstop, plus we don't want to have to pay the extra fee that comes with a chaperon. The airline is Major US Airline if that makes a difference which I'm sure it does.