Don't sweat it too bad. If you can pass a Navy PFA with decent scores (10:30 run) and 5+ over the need for pushups/curlups then you'll do fine at OCS. There are several um...
stressors at OCS to keep you motivated to do what you need to do.
I came into OCS in pretty bad running shape, and thanks to that and partially to the general stress of indoc week, I absolutely sucked on the in-PFA run. I ran like an 11:55 or something (I'm 24). The pushups and situps were good. Trust me, we didn't run at OCS as much as they used to, but by the time I was on my out-PFA, I was running 9 flats easy and maxing pushings/curlups.
Just make sure you pass the in-PFA or you'll be off to see my friend "Master Guns" in 'H' for 3-weeks to get you into shape.
As for breathing, the "in 2, out 2" works well, but the best thing for me is to
not think about it. If you're running and you're thinking to yourself,
Oh man! I'm out of breath! or
Oh God! My legs are tired! How much further?!? etc. you won't perform as well as if you would if you just focused on a rhythm for both your pace and breathing. I'd just jump in the runs and get right behind my DI and stare at the back of his head and force myself to stay with him. The whole OCS atmosphere and running with people will help you out, trust me.
Until then, just keep running, and focus on improving your times. I'd make sure to be able to run a steady 2-2.5 miles without stopping. You might try alternating some intervals in there, where you jog 90 seconds and sprint your guts out for 30. That will develop your fast twitch and also get your heart used to pumping then going steady, i.e. better cardiovascular shape.
Sorry so long-winded, hope this helps & encourages.