Best thing to do is work on your cardio, do push-ups, pull-ups, and crunches/situps. Do Push-ups and Pull-ups three times a week. Crunches 5 times a week. Run three times a week. Run at least one mile over what you will be running for your test for distance runs and alternate those with sprint interval training (sprint for thirty seconds, jog for two minutes, repeat for about 20 minutes).
If your city offers it, go to practice fitness tests as often as possible. Cardio will be easiest to get up. You won't gain much muscle mass in that short of time, but doing body weight exercises will help a lot. Remember to include at least one or two rest days per week, so that your body can rebuild. Also, don't exercise the day before your test, use that as a rest day as well.
Good Luck!