First of all, don't listen to dez, who obviously knows nothing of which he speaks. It's federal law enforcement, not 24.
Secondly, welcome to the fraternity. Heading down to FLETC? Believe me, the shitty food, ugly chicks, and sand fleas are much worse than the physical stuff. I know...I've been through twice, and very little of it involves fond memories.
For the most part, bulk ain't gonna do you a bit of good. Work on your upper body so you can max the BP, but even at that you score the most points at something like 1.5 times bodyweight. You don't need to be Anthony Clarke to get your points there.
Other than that, work on the specific events, particularly the shuttle run. I'd include a little more aerobic stuff, too, since besides the 1.5 mile run they're gonna have you running in the heat almost every day.
For the flexibility, we found that using partner drills help. Assume the position, go to max stretch, then have a partner g-e-n-t-l-y push you a bit beyond your range. Relax into the stretch. Rinse and repeat.
Another thing is don't max out your first time through the test. The instructors like to see improvement, so don't blow your load.
p.s. Another point, regarding academics. "71, badge and gun." All you need to do is pass. I was distinguished grad/valedictorian on my two times through, and it's all forgotten by the time you drive off the base. Relax, pass the courses, but have fun.