Do you have a jazz instructor? You'll need one, IMHO. I started from classical and then moved to jazz, and there is a huge difference. A good instructor can guide you through a lot of the idiosyncrasies.
You should probably commit to a method of some sort. I really like this one:
Amazon.com: Joy of Improv, Book 1 (Piano) (9780793578771): Dave Frank: Books
But others rave about the Mickey Baker books:
Amazon.com: Mickey Baker's Complete Course in Jazz Guitar: Book 1 (Ashley Publications) (0073999104240): Mickey Baker: Books
Or, you might consider signing up for online interactive lessons. Jimmy Bruno's institute is very well regarded and is opening back up after moving to a new site in just a couple of weeks.
Jimmy Bruno Jazz Guitar, Music Educator, online guitar lessons
As Mr B states, definitely focus on chords and comping (accompanying) for now. That'll be your main function in school band.