You qualified for the Under-19 sectional championships (that's why it's the "sectional qualifier"). That means you get to fence in your sectional (what, North Atlantic?) U-19 championships which are this weekend in Western New York(your section web page is at
http://www.prisedefer.com/nasusfa/). At that competition, you can qualify for U-19, Div II, and Div III championships. (if you qualify for U-19, you qualify for Div II, and if you qualify for Div II, you qualify for Div III). If you didn't register and compete in that, you're out of luck. They should have told you this at your sectional qualifier and given you an application for the tournament; you should check into the appeal process with your division and the USFA office.
If you go to the USFA web site (www.usfencing.org) the first item under current news right now is qualifying paths, because you're not alone in being confused.