You need to be talking with your
cross country coach, and following his training plans.
For a good website about running, check out
www.runnersworld.com for the cross-country distances. Also check out
www.elitetrack.com for some good stuff on the shorter distances' training (1,600 meters and less).
You've indicated you haven't trained this summer so that's your problem. And you've gained 12 pounds. I'm guessing since you haven't trained that alot of that 12
pound gain isn't muscle.
How bad do you want it? If you want it bad then get to work. You have alot of work to do and a lot of catching up to do.
Good luck.